sorry to hear you've been through the mill, mopsy. It sounds like you came to your decision after lots of heart searching, and I hope you feel better now you have made the break.
Lizzer, I can totally understand where you are coming from because I have had similar experiences (yes, two or three times!) to bayleaf's in my twenties. I am still friends with two men who seriously broke my heart and yes, I did sleep with them after our relationships had finished. They have been part of my life for twenty years, if now only now a small part. My husband has met them and knows about them. I have met their current partners. For years I felt the odd twang but now I don't.
I think that if you share time with someone really extra special, then why not try to retrieve a friendship when the relationship ends. I knew when it was time to stop sleeping with each of these exes - and then it was a lot easier to say goodbye to that part of our relationship. No pun intended, but this didn't happen overnight.
However, IME, if your boyfriend is an ex, you must never be lulled into forgetting you are a free agent. Sometimes the boyfriends I saw as exes liked to think my life had stopped still and I was still 'theirs'. While not rubbing it in their faces that I wasn't,I never let them think I was putting them first as before.
However nice it is to meet up, IMO your absolute priority is to make new friends, see if there's anyone else around who you like, think about your future and generally get on with your life. Having your ex as a friend can be a boost - you know they still like you and you are not obsessed with wondering what they are up to, but you have your freedom, too.
It depends on you, I think. You'll either find it easier to make a new start knowing you're on friendly terms with your ex, or you won't. Just remember in this, you come first.