How...can someone help me with this story?

I think you should create more drama. If her boyfriend really didn’t care, he wouldn’t have gotten in a fight with him right? So, he cares, that establishes him as the “good guy” of the story, which also kind of means that the guy she slept with is the “bad guy”. But instead, I think you should switch the story up a bit. Define the guy she slept with’s charachter more, aka, make him a “good guy”(make up an excuse for him for why he was at the party or somthing). Take him out of the wrong so she is eventually torn between the two and has to choose. It should’nt be like oh he(party guy) just made a 1-time- mistake and he’s a perfect little angel, no no, that’s the job of her boyfriend. He(party guy) has to be only temporaraly in the right; if he keeps making mistakes throughout the story, then you’ve created a situation in which the reader is curious to find out who the heroine chooses. But it leaves them room to root for whichever guy the reader is hoping she chooses. Define BOTH of their characters so its harder for her to choose. Lol, I know I’ve ranted on a long time, but I figured I might as well have fun imagining it while I was at it =) in any case, I hope I’ve helped, and good luck on your story!!