'AITA for showing my neighbor evidence that his fiancée might be cheating on him?' UPDATED 2X

"AITA for telling my neighbor that his fiancé might be cheating on him?"

I often walk my dog around the same times in the afternoon and the evening. Almost every day for the past 2 or so weeks, there’s a strange car from ~8:00PM to 12:00AM (my neighbor Matt works graveyard shift). I don’t really think anything of it (because who really concerns themselves about a neighbor’s car), but like an hour and a half ago, I saw Matt’s fiancé talking to some dude.

They didn’t really notice me (or if they did, they didn’t care) as I was walking my dog, but I distinctively heard her say “bye sweetie” and gave him a kiss. Well I despise cheaters so I loitered for a bit until they went inside and then I took a picture of the car and texted a picture to Matt. I said and I quote,

"hey dude, sorry to bother you, but there’s this car that’s been here every day and I saw some dude kissing your girl. Just thought you should know, sorry if I’m intruding or anything. Hope i'm just overreacting."

He didn’t say anything yet (I sent it 7 minutes ago) but I’m playing the situation in my head and wanted to ask if I was an a$$hole for sticking my nose into their business?

Edit: He responded saying "Are you sure she wasn't hanging out with a girl". Apparently she was supposed to be hanging out with her girl-friend. I said I'm 80% sure because they have short hair (It was night time, after all) but I KNOW I did see her kiss and say bye babe. I have to go to bed at 11 but I'll try to update as I can until then.

What do you think? AITA? This is what top commenters had to say:

Kevrn813 said:

YTA. You had incomplete information and jumped to a conclusion which you then shared with your neighbor. It sounds a little irresponsible and like you were looking to start some drama. Regardless of whether or not you actually caught her cheating, you decided to wedge yourself into someone else’s relationship. Which is generally frowned upon behavior.

BellaBlue06 said:

Yikes. Maybe wouldn’t have said all that in one message. Maybe start with hey there’s always a car parked here everytime when you’re at work and I saw something I thought was suspicious just wanted to know if you were aware. I would say NTA if the other person is cheating they’re the a$$hole. But the message was pretty abrupt

And [deleted] said:

YTA. You're not certain what's going on, stay out of it. Nosey neighbors are the worst.

End of story? Nope.

He later shared this major update:

She came to my door (I have a sill that opens up) and she starts screaming at me to mind my own business and why would I be so cruel to her and I don't even know her and why would I try to ruin her marriage and what I did she ever do to me. I said I'm sorry; I just don't like cheaters, and if she does not leave now, I will call the police.

She said "let them come" and that she was going to call them for "harassing" her and to go to hell for trying to destroy her life for nothing. I start recording her on snapchat and putting it on my story laughing (okay I might be TA now) as she's tantrumming and crying and screaming. She said "she'll be back soon" and left. Now I'm glad I told him so he can get away from batsh!t insanity.

...and then, a final update:

So I’m going to leave this up as a lesson as myself and to others. I acted like a HOOMUNGUS douche-cannoe and I deserve to be shamed. Apparently his question was supposed to be literal. She was supposed to be hanging out with a actual girlfriend; apparently she’s bi and he’s straight and they both could have girlfriends.

He expressed reservations in the past because he didn’t want her to sleep with another guy and she assured him that she’s completely okay with girls. That’s why he was asking “am I sure she wasn’t hanging out with a girl”. So when I said 80%, that really pissed him off, and he called her and told her off.

They had a huge fight and after they hung up, she came to me and told me off. That’s when I started laughing at her and recording. She was pissed off and humiliated and she left, and shortly returned with the “guy” I saw which was a pretty, butch-looking girl with short hair. Soon afterwards, a police officer came and she said I was stalking and harassing her.

She told him about the photos and the videos and the snapchat story and he asked to see my phone. I told him no, I know my rights, but he said if I didn’t, he was going to make this a lot bigger of a deal than it has to be so I eventually caved. He did see all my pictures (the 5 or so of her car, a couple I tried to get a glimpse in her window, and the videos I had of her crying).

He asked me what the heck I thought I was doing, and I tried to explain my side of the story. He wrote up a report and went to go talk to her and that was a couple minutes ago. I’m scared shItless that they can press charges and IDK what happens from here. Just wanted to share this and somebody can learn from this experience.

In the words of commenter effyocouch:

YTA. I really hope they press charges because you deserve it. You absolutely invaded their privacy. You took it upon yourself to become some sort of anti-cheating vigilante and I’m thoroughly glad it backfired on you. I hope you learned your lesson.