As 93Lowrider stated, you can be proud of yourself for even going there. That can be a very hard situation to deal with. My ex just recently has a new partner and introduced them to the kids, and she seems to feel the need to let me know about it every opportunity. We haven't had any family gatherings yet, but I let her know I was happy for her even though inside I realize that this person might have a major impact on my kids and that brought up some emotions.
How have I decided to deal with it ultimately?
To Let it go, and keep trucking. I will only focus on the kids, and every time I see them in the future, whether her new partner is there or not, I'll let the kids know it's about them.
I realize in my own situation that since I have no say in who she partners with (unless they harm or negatively influence my kids in some way and I can prove it), it's pointless to let emotions creep up and affect me when it comes to her. But when you focus on the kids and make it about them, it will accomplish two things:
1) You can occupy yourself with something that's positive
2) Your kids will appreciate you for it one day.
Your emotionally situation is about the long-term end result, which is about the kids.
Good luck. I know it's hard sometimes, but you'll feel better about yourself in the end.
Life with Divorce: http://www.lifewithdivorce.com
A personal blog dedicated to sharing my experiences, lessons learned, and advice on navigating through life after separation and divorce.