What amazes me is that it takes two to tango.
If he is making a play on you, then from the outset you must have known that he was a married man looking for some sidelong action whilst he wasn�t getting any at home. It happens, most women will tell them to eff off.
If you made a play on him, then sorry love but you are the bad �un.
I completely agree with jno, whilst my wife is heavily pregnant, affection, attention and hows-your-father are way way on the back burner, but I would never cheat on her. Once the baby arrives he will go all goo-goo-ga-ga and cast you aside like one of the nappies he is stocking up on.