I've been off the boards and forums for a few years, going through my own growth opportunities and learning quite a bit about myself..
it's funny that my first visit back, I'd see a post about letting go of the ownership and letting one's primary partner see their other love more than x amount of time...
SparklePop had so many good thoughts that I need to re-read that for myself and my own growth! (thanks for that)... I can't say it any better, especially since I'm struggling with the same thing. It really comes down to trusting that your own relationship isn't going away, and just letting go... (not as a doormat, but as someone who owns their life and feelings, but doesn't own anyone elses)
good luck to you