Yeah, love hurts(i know, this ain't helping hehe). I am surprised you are taking it so well. But messing around with people in relationships is unfair and unwise. I presume you love him, but it is really not your fault at all. This situation would not arise if he had any balls, sorry to put it like that. I hate people who are so indecisive, he should have either leave her or you before it became a thing. Sadly love and lust know no logic. Learned that the hard way, yes i did.