Jason's girlfriend has a fetish of calling him "Matt" when they have kinky sex, but when he brings up doing kinky things as Jason she's "not that type of girl". Turns out "Matt" is her boss she's been cheating with. Jason dumps her.

TL;DR: Most of you were right, she was sleeping with Matt.

Here is a link to the original post: https://www.reddit.com/r/relationship_advice/comments/9x4b5s/my_gf_likes_me_to_go_by_different_names/

I want to start off by saying thank you to everyone who responded.

After I made my post, I waited 2 days to say anything to her because I wanted to get as much input as possible. I also took that time to prepare myself to separate.

I started reading comments right after I posted. I replied to a few but after so many telling me that she was cheating on me with me, I started to feel sick. I called my boss to ask for Friday off for personal reasons. I spent the day driving around, looking for potential apartments. We don't live together but I wanted to make sure if things went bad, she'd have a harder time finding me. We also have some good memories in that apartment and I think I would be sad if I had to continue to live there.

This brings us to Saturday, the day I promised myself I would say something. I invited her over for breakfast but instantly regretted it because I was getting so nervous that I completely lost my appetite. She walked in the door and instantly knew something was different. I was hoping to ease into it, but I ended up blurting out, "I met Matt Blank". She tried to act casual about it, but I could tell she didn't expect me to know about him. For the next 3 or so minuted things were calm, I talked about how I see the past 4 months completely differently. She started to cry and say she was sorry, I don't mean some tears but full on ugly crying. I told her I'm going to work on forgiving her, because if I don't I think it will eat me up inside. I won't forget what happened but I'll at least try to move on. She started to talk about how she'll work on building my trust again. I interrupted her by saying that that isn't necessary, as we were no longer together.

If I wasn't so emotionally crushed, I would have been amazed at the transition. She started begging me to give her another chance. I stood up and went to my room to grab a few boxes of all the gifts she gave me. I told her that I had already made up my mind to break up with her. After some back and forth, she realized that I was serious. I knew the exact moment she knew I was serious because she went from crying to yelling. It started off with insults and when that didn't work she tried throwing the truth in my face to hurt me. It started off that I was fat, ugly, lazy, stupid, and I had a useless job. In the middle of her tirade, she said Matt's dick was way bigger than mine.

As she was yelling at me, she ended up saying what happened between the two of them. I'll summarize below:

She started sleeping with Matt 3 years ago, they were on some sort of work trip and ended up drunkenly sleeping together. From there it went from once in a while to once a week. Matt called things off 4 months ago because he met a girl. I think she was using the vacations because she missed being with Matt.

I don't really remember the rest of Saturday. I spent Sunday with my friends which helped, I told them what happened which was nice to get off my chest. I went to work as normal yesterday, at some point in the day she slipped a note under my door. I'm not sure what it said because I burned it.