I used to be totally allergic to the idea of sharing. I felt really insecure about it, and with good reason, at times. However, I was involved with one fellow who made it a possibility for me, largely because of his attitude. Not only was he an excellent communicator, but he was very sensitive to everyone's needs, checking in and double checking, making sure everyone was taken care of, etc. I knew exactly where I stood with him (#2; his primary was in another state) and I could trust that he would seek out and take care of my needs, and everyone elses' too. It was really hot to hold her legs for him, spread her pussy for him, hold her from behind and help her arch her back . . .
Now I'm married, and we have a bit of an open relationship -- we can bring home a girl once in a while, provided we're both in on it. This has been one really good way for me to fulfill my desires for girls. (Frankly, they're just nicer to look at!) But we have really clear rules, and knowing I can trust those makes it easier. For us, it's a one-time only deal. We also monitor for letting that desire get in the way of our commitment to each other. For me, the stability of our relationship, and the trust I have, makes this possible. Plus, I'm the one who gets to initiate it, which helps to reinforce that I have control over the experience.
If you're interested, and you feel that your relationship is in the right place to try it out, I'd encourage you to try picking someone up for a night, just to see how it goes. Be sure the rules are really clear, and also that the person you're picking up knows what the situation is, to be fair to everyone involved. When you're in the right place, it can be super hot; when you're not, it can feel awful. I hope you keep us up to date! Good luck exploring.