I'm living through pretty much the same thing only in reverse. My wife has started dating a guy who is a real loser and it is so hard to just be happy whenever I am around her. Not only do I feel hurt by the fact she is with someone else, but I also have to deal with the fear she could be really hurt by this jerk. Just hang in there, patience is absolutely the number one thing you need to have. Find something else to occupy your time and your mind. Be with people who make you happy and don't let yourself get stuck thinking bad thoughts. If you feel bad when you sit back and reflect, then don't do it. Stand up and look forward.
I am looking at this OM my W is living with as an opportunity. I try to turn it into hope instead of doom. In my case, she gets to see what living with a druggie dirtbag is like and I can only shine in comparison. That makes me just want to shine all that much brighter. When I start to think negative things about the sitch, I shout at myself in my head "STOP!", find my happy thought again and get back to working on my shine.
Believe me, I know how hard it is and how much energy it takes, but it is the right thing to do. Enjoy what time you get with him and make sure he sees that. But you should also try to find a way to enjoy the rest of your time too so you don't get wrapped up in feeling bad. It is a lot easier to be happy for him when he's there when you start out happier before he gets there.
