I dont see how the guy is doing something immoral.
She knows she is married to someone else.
She knows that she is pregnant with (maybe) her husband's baby.
She all but jumped the guy. He was happy to oblige.
If he were married to another woman then I would say the dude and this broad deserve each other.
But as far as I am concerned the guy aint doing anything wrong.
Everyone in the room was a consenting adult. If this broad shows up on his doorstep a few months from now because her husband kicked her ass to the curb, then I would say he has a problem on his hands.
But short of that - I am officiallly cyber-patting the dude on the back and saying, "Rock on!"