'AITA for cheating on my unfaithful, absent ex-wife with her sister?' UPDATED 2X

"I cheated on my wife with her sister."

I know the title sounds bad, but I need to get this off my chest. Me (35M) and my wife (34F) were childhood sweethearts, we did everything together, and she was the love of my life. I proposed to her when i was 20. I thought it was the right time, so did she. When I was 26 and she was 25, we had our daughter. We were so happy, she was the one thing our life was missing.

We were such a happy family. Then a few months after the birth of our first child, she got pregnant again. Again, we were so happy, now we had our little family of 4. Before anyone asks why we had kids so young, after high school i got my degree in accounting, then i went to work for my dad.

My dads company is big, i was able to make a lot of money, and yes when we got married we agreed to sign a premarital agreement. We went on dates very often, and our bedroom life was amazing. I showered her and our kids with gifts and flowers 3 times a week. We had a big house. I was able to her her dream life we would alway talk about a lot when we were teens.

I thought we were happy, yet she still cheated on me. I found out she had a hookup app. When i confronted her about it, she didn't deny it. She said i was always absent and she didn't have a way to be fulfilled. I wanted to leave, but didnt for my kids even though my pain was too much to even look at her. We went to counseling and we did ok for a while,

but one day maybe 2 months later, she said she was hooking up with guys every night. She even had a few guys over at the house, and in our bed, in the house i paid for. My kids were now at this point 8 and 7. We knew divorce would be hard on them since they loved us both so much, I didn't want them to have a tainted image of her. Through my grief and pain I stayed, but I moved her into the guest bedroom.

You're probably wondering where her sister (30F) comes in. Well throughout all this, she was my rock, my family wouldn't have understood my pain. My wife's family always favored her, because her sister was the ‘mistake’ baby. I still loved her, but i didn't know she made her sisters life hell. My wife was barely home when she moved into the guest bedroom.

Now our kids barely saw their mum. Whenever they spoke to her she was either rude, cold or ignored them. When she came home she would get something to eat, drink and go to her room and stay there. So my wife's sister was there for our kids. She would be at the house a lot. She picked up my kids and did things with them. She was also home when my wife was home, but didnt care.

After 2 years of this, my kids started to call her mum. She didn't want them to if they didn't want to, but they wanted to, which made me happy, they had only spoken a handful of times to their mum, by now they were used to it and so was i. Me and my wifes sisters would spend a lot of time together and I loved it, so did she. Now this leads me to the current situation.

So I had booked a trip to Fiji for me, my wife, and kids. My wifes sister wanted us to try and fix things. Which I tried to do for the first year, but I stopped trying since she wasn't. So i went to my wife and told her about it. She just yelled at me and told me to f off and that she wasn't coming, and i kid you not, referred to her own kids as, ‘those little shits’.

This sounds like she knew about our kids calling their auntie mum. If she did know she would have thrown a fit. She said they weren't her’s anymore and it was a mistake to even have them. This threw me off but i did not persist. So i asked my wifes sister and told her what happened. She said yes and we arrived last week. It's been amazing.

Me, my wifes sister and my kids have had a blast. They love her and this makes me so happy knowing they have a mother figure throughout all the drama of the past 3 years. So this leads me to last tonight. My kids met another family with kids, so they spent the night, which left me and my wifes sister alone. We talked about the kids and life in general, with the mood and atmosphere.

We could both tell something was going on between us, and i kissed her. She stopped me, asking if i really want to do this, and that this doesn't seem right. I told her i did and i feel like we could both feel it (we didn't share a room, my kids shared a bed and i had one next to them, my wifes sister had the master bedroom). So we ended up sleeping together.

Yes i know its bad but nothing had happened like this before, the setting really set us up. So right now i'm lying in bed next to her typing this out, about to text my lawyer. She's still sleeping. I just needed to get this out. I know not many people will read this but it would be good to know if one person does. Thanks.

First update later that night:

So I deleted my original account because I realised how wrong I am for not divorcing my wife. I don't know who's gonna see this but it's worth a shot I guess. So I’ll clear up a lot of confusion, yes I let my kids stay with a family they just met because like I said there were other kids there not just mine and the family, yes my wife stayed with us because she didn’t really have anywhere else to go when she cheated.

So because of my infidelity and hers as well, I am entitled to give her a sum of my money, which I don’t give a damn about because I’m very well off, unlike her because she doesn’t really work, so I got home this morning, right now it’s in the afternoon and we went straight back to my house, well when we walked in my wife was waiting on the couch, and she was very upset, She asked why the hell I brought

her sister to the trip because I could have just discarded her ticket, well no I couldn’t have they cost a fortune and even though I’m well off, I teach my kids the value of money and I thought she knew that too? I thought wrong obviously. Well I told her this and asked if she could calm down so we could talk, she wouldn’t calm down unless her sister was gone so I told them to wait in the car.

So I sat down with her and asked her if she had guys over when we were gone, of course she did, at this moment what a few of you said about my kids maybe not being mine sprung into my head, so I asked her, she said that she had slept with one guy a little before my daughter was born, my stomach dropped, she said she didn’t think it was his because of how much my daughter looked like me

but also said the guy she slept with kind of looked like me, so I’m planning to get DNA test done on both my kids. I told her after that I what a divorce and to my surprise she got upset, not the kind of upset when you get up and start crying, the kind when she lowered her head in disappointment, I saw in her eyes she realised what she had done,

how badly she screwed up her relationship with me and her kids, not to forgot her sister as well. She said she was so sorry for how she treated me and hopes we can work through it, I thought about it because I saw the girl I fell in love with again, the girl who’s laugh brought me happiness, the girl who knew how to make me smile, but then I remembered what she put me and the kids through.

So I stood up, told her there’s no way in hell she’s getting another chance, and if she really wants to see the kids she can but on their terms, I told her my lawyer would be in touch and I would be open to renting her a temporary room until the divorce is done, she said she would like that, I let her grab a few of her stuff and watched her to make sure she didn’t take anything of mine.

I called her an Uber for wherever she wanted to go in the meantime, I also told her I’d let her know where she’d be staying. She left rather peacefully but kept her head down on the way to the car. My kids came out and asked me what happened. I told them mummy’s not staying with us anymore but if they want she can come and visit them whenever they want to see her, I told them to go upstairs and unpack,

so this gave me time alone with their aunt. We sat down and basically talked about everything, what happened on the trip and what will happen now, we agreed to try and start dating, but after my divorce is finalised, which is best for the kids to cool down, they will see their aunt whenever they want but she is not going to live with us, also she isn’t married I wouldn’t be doing this with a married women.

So yeah this leads me to now, we just finished a paternity test at the clinic, I’m so nervous to find out the results, I’ll update when I get them. Thanks.

TLDR: I grew a pair and filed for divorce on my cheated STBXW after I slept with her sister.

Two days later, he posted this second update:

I got the paternity results back and both kids are mine, I am over the moon that these kids I love so much are 100% my blood. My kids and I have all started counselling, with 2 sessions a week, their first session was after school and it already seems to be helping,

now onto 2 topics I think everyone wants to know about, my ex wife and XSIL. I’ll start with my ex. I got her a studio room last night. I don't know what she does during the day but I don't care. We have only had a little conversation, I’ll post it if reddit allows me to since I am allowed to. The gist was about our kids and divorce. She has signed the papers my lawyer sent her.

She has told me she will fight me if she wants to keep her kids away from her. She has been harassing me, my Mum, Dad, Siblings and their children when I ended our conversation, I have proof like a few of you suggested. With how everything's going ATM, looks like I’ll be getting full custody of the kids. To the person who messaged me about my ex maybe having a mental health issue,

there's none I am aware of but she may need to get a test done due to the way she has been acting. My kids don’t want to see her right now and I don’t blame them. I will try to get a protective order in place before the court date which will be decided on in the next few weeks/week, but the actual date will most likely be in a few months.

I’ve taken all the money out of our joint account but have sent her some to live off and enough to hire a lawyer. Now onto my XSIL. So we have talked once, that was before I wrote this. My kids really want to see her so we have planned a day for them to hang out with her Friday after school. I've read all the comments about not getting into a relationship with her, I did say I wanted time to see what I want to do,

but again, we spent the night together and I don’t want her to feel used, so I told her my feelings and she was extremely supportive and understood, she told me how she feels and I am happy she doesn’t feel used. We will not be hanging out but I will see her if I come to collect my kids and she's there, which is fine, she's a great influence on them and she is helping them through their Mum and I’s divorce.

Right now I’m sitting outside on the deck, we ordered their favourite take out and I’m watching them goof around, it's great to see them so happy. I don’t know when my next update will be, but I will as soon as I can. TLDR: Now ex wife has been harassing my family, made boundaries with XSIL and life is looking up for once.