What is it about being the ex that makes you feel like you have some sort of prior claim on a guy? Like, hey I was important to him at one point!!! Or that even if you don't want him whatsoever, to see that he's moved on is kinda sad to you and makes you a little jealous? Anyone else have experience with this?

*sigh* Yup.
I was engaged to a great guy and he broke it off in 2005. It was hard for both of us, especially me, but to this day we're very good friends and hang out and talk regularly.
He's been with a new girlfriend since 2007, and just last October they had a son. Now I myself never wanted kids, which is part of the reason why we broke up. BUT. To this day I have problems being around his girlfriend. It's not that I haven't tried. But she seems to despise me. When they started going out together she sent me a long email telling me that if I was going to be friends with my ex I needed to assure her that it was with good intent and that I wasn't going to try to sabotage their relationship. I was livid, and terrified. First, why in **** would I want to go back to someone who dumped me after promising to love me forever? and 2nd, you have to be really insecure to say something like that to a fat girl who doesn't have much going for herself.

But anyway, my point is, when I'm around them TOGETHER, I'm very nice to her, even if she's not to me, out of respect for my ex, my friend. But I always feel like she has this sense of entitlement that should actually be mine, and I should be the one who's pissed off. Because after all, I was there BEFORE her.

Re: her email. she is obviously very insecure in this relationship. And jealous as well since he was with you first. She is probabvly giving off vibes, that she wants you to stay away. I think it might be better, as hard as it is to do, to break off your relationship altogether, Move on.

I have thought about it, I've ever talked to him about it. But I don't see a reason to break off a decade-long friendship over something as petty as a jealousy fit. He agreed. At the same time I never imposed myself to his girlfriend, I know she doesn't want me around.
I'm in another relationship and couldn't be happier, and there's reasons why I'm not with my ex anymore, and why I wouldn't want to date him anymore. But just because we're not IN LOVE anymore doesn't mean we should cut off all contact. After all, we started up as friends.

Maybe it looks different from the "current girlfriend" point of view...

See, it's one thing to be nice to the new gf, esp if it's out of respect for ex bf. If the two of you exes are fine with it, and you truly are nice to her and bear no ill will, then it seems like it is her own insecurity. But since they have a child, it does get a little cloudy. Maybe you need to have another talk with her, face to face. Try to eventually be friends with her too, not just nice out of respect. Might help?

Anyone have experience being the ex who can't move on? Not friends w ex or ex's gf, but still try to talk to his family and remain close? Sad and jealous that he's moved on and is happy?

i have experienced this. and even though i'm mostly happily married and i have been w/ my husband for 10 years - there are a still a few guys from my past that... i guess i never got resolved. one of them recently got married and i was really sad about it.
it's not so much that i want him as... i guess once we break up i think he should stop existing all together. lol not that i want him dead, just that i don't like to think of him moving on or anything.
i had one ex i never got over. i just try not to think about it cause it still upsets me. it's not him that i'm not over necessarily- just the situation and the pain from then... it's been a decade and it still hasn't gone away. i doubt it ever will.

My OH and his ex have been divorced now for over 7 years and she still harrasses him. We actually had to change his phone number and then recently she sent him a letter and it had stuff in there about me and I don't even know how she found out about me (she lives over 1800 miles away). I still can't figure out how someone can't get over it after 7 years. I understand they were married but she needs to move on and try to be happy herself, you know?

I've experienced that, for sure. I was engaged to a guy and we broke up 10 months before our wedding. Four months after we broke up he was going on and on proclaiming some new girl to be the love of his life. He then proposed to her 8 months later. He seems to be really happy now, and I kinda hate that. Our relationship was not a healthy one and I'm glad that I'm not involved with him anymore...he's not a good person and I don't want him. Yet, I can't help but feel a slight tinge of jealousy and even sadness when I see them together. Sometimes I find it a bit bothersome that he somehow still has a hold on me. Ugh.