Why did my husband ask about her sex life with her husband?!?

It's obvious.Men want to be the best,to be on the top,so he compares his sex skills with her husband's.He want to be sure that he is the best and he needs confirmation.I wouldn't advice you to leave him or not,it's up to you.But I would say that you have to stop tormenting yourself by seeing what he does and stay silent.You don't deserve this.Anyway,I respect your wish and I won't go further.