You know, always worrying about someone leaving you will not stop them leaving you. These worries are pointless as all they do is fill you with sadness and make you feel bad. Absolutely nothing you do will stop them leaving you if they want to go - but by being fun, kind, loving and relaxed will make you too irresistible to consider leaving!

I think its great that you realise that you need to alter your behaviour, its so very hard to admit a flaw. Perhaps try some CBT to get yourself into a more positive thinking pattern. In the meantime, try and count to ten when you next feel yourself worried or feeling jealous and ask yourself if there is any proof for you to feel this way. Try to remember that he is with you and nobody else, but also try to remember that he is allowed friends too.
I think you have a very understanding fella and he does sound lovely too and I hope you guys work it all out :-)

Good luck and hugs.