I'm currently in the same place you are puddi, my ex is now living with another man, pregnant and they've got my kids living with them in Germany and for reasons I can't quite nail dwn, it really lashes me emotionally to see them together. It's not that there is anything that really could be salvaged between my ex and I, it was a wonderful realtionship for the years it lasted, but too much went on and now it's over, but there is something about seeing people you have loved who are deliriously happy and making a family with someone else that makes you feel as though you'll never quite recapture that yourself.
I feel very strange when I see them, but I've realised that actually that the old saying ' what doesn't kill you makes you stronger' and you are a very strong, very nice girl, whose clearly moved mountains to survive well with her kids, and somewhere out there is a man who'll recognise that for the pearl that it is, and then everything will come up smelling of flowers for you for a change.