I don't think that trust can be 'regained'.. you have to be open and willing to trust again as it can't be earnt.

I couldn't have imagined my life without my ex in it either... We tried so hard to be 'friends' in the end I would say that if something really went wrong in my life he would be there for me but that is as far as it goes now.
I do miss him, I will not lie, but he has his own life and now I have mine... clinging to the past doesn't help anyone... the past is just that past.. the future holds much happier times for you xx