Being cheated on hurts deep. It's one of those betrayals that affects people in a very major way so it's not that far out for yu to continue to be angry about it for awhile like this. I've been there... it crushes you inside. being left is one thing, being unloved is another but being cheated on adds on the layer of betrayal, to those things. You're hurt, feeling lied to/deceived, betrayed, broken hearted, angry... its just one of those things that kind of hits a lot of nerves at once. Trust me, it does pass, though the betrayal will affect you for a long time if not for good. it really throws our sense of trust off badly.

*hugs*