A large part of the event in this game is locked behind and/or tied to certain traits. Breaking up with a man if you're a weak willed, shy, nice and romantic character, whom isn't picky about any sort of men, is extremely hard. While it's much easier if you are a strong-willed, cold blooded bitch with the aromatic trait, who despises all types of men and generally dosn't get excited by anything, which means you cant ever fall in love with someone and that makes it very easy to unfriend and breaking up with people.
Since the game is all about traits, ofc we have to factor in the npc traits too. Some men likes it when you sleep around, so even if you do and are discovered they don't care, rather they like it which makes it extremely hard to break up a relationship with those kind of guys who likes it when you sleep around. On the other hand if they are have a selfish or jerks personality without that trait, they'll get angry and if they don't love you pc enough if you admit to cheating, they'll end the relationship themselves. Also, there is an event if you get pregnant with a man and if they love your pc enough, they ask you to leave your current BF for them. Then we have the scene where the boyfriends jerk friend shows up, where you can side with him and effectively make your BF leave while the jerk stays (and becomes your new BF, cant really remember it fully). I "think" that also works if you refuse to accept it when an npc you've slept with blackmails you and wait for you BF to arrive. I'm not entirely sure about the last part though, it's been a few game versions ago since I went through that particular event myself.
So yes, there is quite a few ways to dump a BF, keep in mind that a lot of them tied to various pc & npc traits. Which makes this game both very unique, since there are so many triggers that can happen due to those traits and the corresponding personality of an npc, which means there are endless possibility's, well in theory anyway. Why? Since a lot of content are tied to pc and npc traits, it's also extremely frustrating if you want to see everything in a playthrough, since you NEED certain traits for both your PC and the NPC, if you do not, you get locked out various parts of the events in the game.