He slept with someone else.

[catfeeder]

First problem is that your relationship was already rocky enough to leave. Bigger problem is that you already knew you couldn't trust him, or you wouldn't have asked this:

 

I asked if he had done anything with anyone else while on this break,

 

When you already know you can't trust someone, why would you expect an honest answer to such a question?

 

Why stick around for things to get worse from there? Or better question, can it really get any worse that this?

 

I'd cut my losses and walk forward without the guy, because no matter what he does from this point forward, what good is it when you can't trust him?

 

Knowing you deserve better is the first step in moving toward everything that's better.

 

Head high.