So so sorry. It is hard for the WS to understand the hurt of the BS.
Look in the healing library as there are couple of great articles there that vividly describe the devastation.
I think you knew all along in your gut that he was lying about the roommate. You just didn't have proof. So it hurts because your worst fears have been validated. It is not easy to reconcile deception and betrayal. You are hurt and in shock and understandably so.
Give yourself a break and don't beat yourself up. You didn't create this. But do allow yourself to feel everything you need to feel. Anger, sadness, despair and hope. All has to come out in order to move on.
The second thing is the Craiglist bs. It is a trigger for you. I don't care if he met up with anyone or not. It is an EA every time he connects with someone that is not you. Period.
He is putting time and energy into a lie and fantasy vs. his marriage.
I suggest IC for you both and eventually MC. But first he has to get to the root of why he chooses to prowl CL for hook ups. WRONG on every level and it has to stop.
Hang in there and be strong. You are better than this and you know it.