I'll try to get an explanation from him first. There would be two or more consequences for this. For example, he either would lie and gave you an excuse, or he would tell the truth but you couldn't accept the fact about it. If he gave you an excuse, done! He's done for it. No excuses for you to not leave because if you gave your trust and he broke it but then still covers up like he is innocent, why should you give him a chance if he knows he could just make excuses for the next time he got caught? But then, if you're the type who could still give him a chance, ask him again, if the same excuse came out although you already know the truth, then it is up to you for your next step. Well, about the couldn't accept the fact, usually because you didn't want to admit your jealousy. Girls especially, they won't admit or confess their jealousy because they know people or their boyfriend would think of them as too clingy and annoying. But then, just talk it out. Say that you're sorry. If they couldn't accept your apology, just walk it off. There's no time to spent on people like that. I'm not asking you to easily break up or anything, everyone has their own way with their relationship. I'm just voicing out my opinion.