To start I want to say that i am by no means the perfect boyfriend or father. In early December a few months after my son was born me and my gf got into a big fight. We ended up breaking up as i felt like i couldnt deal with the pressure of the relationship, school, work, and our child at the same time. I broke down and dropped out of school. I almost lost my job and our relationship fell apart. Over the month before my so and i reunited i did nothing but lay in bed and rot. Fast forward to January and my so texted me asking to work things out. We did end up talking and working things out making it clear we both wanted eachother and to raise our son together. This is where things start to fall apart. We talked about what happened over our extended break as i will call it and things were going well. Than i found messages of her and some other guy with her saying he was “so hot” and asking “are your other girls as obsessed with you as i am”. I confronted her with this as she never mentioned it. She ended up telling me that she was just using him to get over me and that she had nothing for him. I noticed she was acting weird so i pressed further and she proceeded to tell me he sa’d her. The problem is i can never get the details to add up. Her sister straight up told me she was lying about a few things but not that she was lying about the situation fully. My gf obviously denies this and says her sister is a habitual liar. I legitimately cant get this out of my head. I think about it every night. I am not trying to claim she is lying. I love my girlfriend with everything i have and i want to trust her. Its not even what happened thats the problem no matter how that night went down. Its the fact that she could be lying and i honestly dont know how to go about talking to her about this. I dont want to bring it up because it makes me feel like im calling her a liar about what happened to her and i dont want to blame her for being the victim in the situation. I have no clue to approach this and i cant keep thinking about it every night.

Sorry for the long post any advice or thoughts would be appreciated.