Should you break up with someone who lied?

You should dump him, who's to say he won't keep doing this kind of thing behind your back in the future? He may feel as if your his "fallback" girl..because of problems he had with his ex. If he truly wants to be with you he should break things off completely with his ex..and that is that. You can always play the "reverse phsycology" on him..and do the same he does, and just wait for his reaction to it. It depends on what you want out of a relationship. If you just want occasional servicing, what does it matter if he cheats? On the other hand, if you want someone who will be a companion, he certainly doesn't sound like the kind of guy who will ever commit. If he can't make up his mind now, what makes you think he'll ever be able to commit to a relationship? It's only been two months, and he's already showing his true colors. What would you expect 6 months to a year down the line, when he doesn't feel the need to be on his 'best' behavior anymore?