To me it is.
Can you really blame a witness teen(older person) for wanting to have sex? I cant. We all "slip" up sometimes.
And drugs, well i CAN blame them, but no one else is really being hurt except for yourself. (and your family i guess)
I just think Adultery is on another level because you're screwing up a relationship and if its prolonged you might have also passed something on to your husband/wife.
Just a thought.