Three some

My husband and I had a three some with one if his friends when we first started dating. Maybe it was a month into our relationship because it was something I wanted to do. We are now together for 8 years married 2 yrs. He mention about having one again a few months ago and I just turned it right down. I told him we are married now and committed to each other

Well today he told me it is something he really wanted to do. I told him I'm not comfortable with it. He asked why and said well you got one when you wanted it

Am I in the wrong. I thought we were more mature now and over that kind of stuff. I am not I'm anyway doing something I am uncomfortable with but does this mean he is unsatisfied in marriage? Or going to cheat or am I over thinking