Hi Valexland,
I can understand how you're feeling, but I'd like to help you see it a different way. So often in our society we paint such a nasty picture about divorce and the battling ex's. One day on Oprah I saw Demi Moore and she was talking about how she and her ex Bruce Willis have such an amicable split. She said not only are they still friends, but actually go on family vacations together (that pushing it) with her new hubby. I really thought that was such a positive way to end things. Now I realize not everyone can do that, especially if there was abuse, but it sure saves alot of frustration and brain energy.
Another way you can think is - you and he weren't happy and he right away went into another relationship. Since he obviously didn't have time to fix them, he's probably making the same mistakes with her - and I bet they aren't as happy as you think they are. If I were you I would be happy he's gone. When you see him be nice and be cheerful to her and I would even go so far as to congratulate them. He will be so shocked because I'm sure he wouldn't expect you to act like that. I bet, when the meeting is over, he'll secretly feel a little disappointed that you didn't seem bothered at all. Don't let it bug you that he's found someone and you haven't yet. You're smart in taking your time and healing first. I'm sure he's already told his fiance what to expect from you - do the opposite and you'll feel better knowing that you didn't let them see that you were bugged. It's all in the way you choose to look at it. Best of luck.