The sex talk in front of your child was not appropiate for sure, but it takes two to have a conversation which you participated in. If you thought it was wrong, why answer your H and why not say "we can talk about this later" or "this is not appropriate"
And knowing the field of mental health care myself and since all of us here aree not privy to all the words exchanged with you and your therapist and I suspect she is not taking a shot in the dark with this one.
He travels, sounds like he wants to talk about sex, you're not giving him sex, he's a man <----- all recipes for one to cheat.
I think you're playing the victim here a little bit