I wouldn’t go so far as to call him a sociopath, but clearly this guy cheated and lied about it. This is clearly a big deal to you, and as you say, he might do it again. Of course, someone who has never cheated and lied can still do so; there’s a first time for everything. What I’m saying is, there’s no way to have a fool-proof, definitely going to work, zero cheating risk relationship.

I wouldn’t be so hasty to throw this away, it seems you’re important to each other. Instead of begging you, maybe he can explain how things are going to be different in the future. What’s he going to do if he meets someone he feels attracted to? What’s he going to do when he’s trapped in a lie and he knows he needs to tell you something that’s going to make you mad?

These are difficult questions. But the way he answers them is going to be worth a lot more than his “You’re the only one who knows me!” or any kind of “I’ll be true forever, pinkie-swear!” That doesn’t really mean anything, you know?

If you give him another chance (and you don’t have to), don’t just let him promise to never do it again. Get him to tell you how things are going to be different, what he’s going to do differently. It’s no good giving someone a second chance if they have no plan for how to be better.

Love is hard. Hope this is useful.