I think it's best to explore the "why" behind how it happened.

Were they both just horny and curious.....or is there a lot of honest caring there?

If it's the former there is no threat to your relationship. If it's the latter then there might be a reason to be jealous.

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Life is too short not to love and be loved....preferably multiple times in one night.

I think men talk to women so they can sleep with them and women sleep with men so they can talk to them. ~ Jay McInerney