Would you ever have a three some with your spouse?

My husband is a very sexual person. I'm also very sexual but I feel like I'm breaking my vows even though it would be with him. Before we got married he had only slept with one other person. He doesn't care whether it's a male or female that would be the third person and said he would be okay with either and would let me personally pick who it is. I'm a very emotional person and feel like I couldn't have sex with someone with out having feelings for them and he feels the opposite. Then I also worry stress about pregnancies or STD's as a result of the three some.