First, congratulations. Coming to this decision likely required some soul-searching that wasn't easy.
Advice in general: start small. At this point you may want to treat him like any other guy you have an interest in. Show interest in his life and interests. But have your own life and interests as well. Don't always be there for him, either. You don't want to seem desperate.
Don't bring up old R issues, but keep them in mind. Keep it simple and don't put pressure on him or become obsessive. His guard will be up if you do. He knows your feelings. But he's been hurt by you once and it will take more than a declaration of your love to open back up to you. He's had to heal and move on without you.
I wish my W would get to your point. I just hope she doesn't take two years to get there. Forgiveness might be hard by then, so go slow and be honest (with him, S, and yourself).
~Mark
Me: 38 W: 34 Together: 9yrs 1st M: may '03 1st D: april '08 1st bomb: june '08 remarried: oct '08 2nd bomb: aug '09 --(W asked for D one week into 3 mo. trial separation which was meant to save our M)