Why is the mc so goddamn cringe? His personality is also kind of inconsistent. A guy who second-guesses himself as much as this guy would never confront her about seeing her with that other guy.
You're right, but I think that is what makes the writing good. Even though she hasn't done anything like that, it still sort of feels like she has because we're seeing things through the mc's frame of reference. When I was in my early 20s, I was a lot like him, and a few relationships felt like this even though I'm pretty sure it was all in my head.