Everyone had said some really great things, I just wanted to add a little from my own experience.
We've been married 16 years & just in the past 8months have we finally opened up about our sexual fantasies. And we talked for so long before acting on anything. But just having those conversations, being as open as we ever had been, brought our marriage to this wonderful level it had never been before. Single best thing we ever did for our marriage.
When we finally got around to finding another couple to play with (which was like 4 months later) I was so nervous! I had all these preconceived notions of what I would like & what I wouldn't. And then I got there, in that situation, and it was so much better. The four of us naked in this room & my insecurities about my imperfect body were gone. No one is perfect & to have another man be attracted to me & want me like that is a pretty heady feeling. I also wasn't sure how I would feel watching my husband with someone else, but it was okay. I knew at that point our marriage was solid, no need to be jealous.
I would just recommend to keep talking. Don't do anything until you feel solid. But try to keep your mind open and be totally honest.
But adding what has become our boyfriend & girlfriend to our marriage has been one of the better things we've ever done.