I agree with what wannabe says and if you meet someone else, Pingu, then your ex-P will in all likelihood experience similar feelings to you.
So sorry that you don't have much support. You really have got it tough.
How do things change? Well, funnily enough, I posted about that on another thread this a.m ("has anyone left their DP when still madly in love?")
The father of three that I got involved with was my most important relatoinship until I met DH, we split because we knew we werent right for each other, but like your ex, he was a bit of a "serial monogamist", and he immediately formed a relationship with my best friend (I don't think he would have let me go unless he had her waiting on the sidelines tbh). So in a way the hurt that his ex-wife had felt when I got together was revisited on me. I am not saying it was "karma" or anything - just that he was just not emotionally mature, and I thought that I could be the one to succeed where his wife had failed (arrogant I know, but I was young). I left him after 5 years because I knew this and knew that he wasn't a good person to have kids with and invest my future in (I knew this instinctively because of what he had done on leaving his wife and kids) but I still loved him. So it was incredibly hurtful when my best friend then got together with him, presumably thinking she could be the one to succed where I had failed... anyway she moved into the house I had lived in and decorated etc with him, became pg by him within a year and I left town.
I was very lonely for several years, then I met DH and am very very happy with him. He is much more suitable for me, we have a shared outlook, he is loyal and reliable and completely depndable (all the things ex-P wasn't) and made me feel secure for teh first time in my life.
Meanwhile, ex-bestfriend and ex-P split after his usual 5 year cycle and when I bumped into her a few years back she was very bitter about him, said he never saw or bothered with his DS, etc etc. I think she has now met someone else and is happy again but it took her a while.
Maybe this is a bit of a tale of "What comes around goes around", I don't know, and I have explained it in very simplistic terms because I don't hate ex-P, I still think he was a nice guy and I don't regret our relationship... but he was immature and didn't take responsibility very well. He now has 5 kids with 3 different women. I think he too is happy now, though, and no doubt has matured with age as I know have I...
Maybe all I am trying to say is that there is sunshine after rain and you will be happy once again.