Overreacting? I think so, but that's based on my own experience. I had a similar experience with one of my best friends several years ago and it's not something he and I are likely to ever do again. The only exception being if our respective SO's got together and insisted on it and promised a special show of their own after. As osuche suggested, find out if it was merely an outlet to get off. That was the case for my friend and I and the last time we had any sexual contact was at the request of our previous SO's.

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Put me on wheels and I'll turn tricks.

Clever? Nah, I ran out of that years ago. But if you find this, let me know, k?
"The road goes ever on..." ~ Tolkien

In memory of my friend skip...
Go then, there are other worlds than these