I'd be hurt if I were you too, but the way you talk about this in this post sounds like you are treating the situation as if you two were still together when you weren't. You really aren't entitled to know the details of his personal life when you two are separated, so I agree that you should be glad he told you at all. And being angry at him for "lying" seems pretty misplaced here ... again, you're treating it as if there was some commitment when the whole point of the separation was to take a step back. He took a step back and you haven't. Honestly,, if you weren't prepared for the possibility of him hooking up with other people, why did you suggest separating? I sense some passive-aggressiveness here and it seems kinda like you dumped him with the hopes of getting a very specific reaction from him, you didn't get that reaction and it backfired, and now you are seeking ways to be angry with him.