Skip; I had a threesome with a very good friend of mine and her hubby a few years ago; I was a bit dubious at first, to say the least (!), but I really got off watching the 2 of them together - and so did he when it was his turn to watch. The biggest turn-on (for me at any rate) was both of us pleasuring different areas of "S" at the same time, and she came longer and harder from that than anyone I've ever known.
Rambling on a bit here, but my point is; IF what occurred with you had happened to us, I think I would have at least tried it, with no regrets - as Sharni has said in other posts, if you don't try, how do you know if you'll like it?

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The selfish, they're all standing in line
Faithing and hoping to buy themselves time
Me, I figure as each breath goes by
I only own my mind