I can empathize completely, i was suspcious of my fiance of 5 years (found some really bad text messages on her cell phone) and then i caught her in our bed with another guy. I actually thanked her for giving me a reason to finally leave her at the time, but afterwards it hurt alot. Best thing you can do is drop his ass, take some time to yourself and id say get to know the next guy you become involved with fairly well before coming too involved. (not saying you did that this time, i just think its always good to get a good feel for someone before you dive head long into emotional attachment).