Based on what you're telling us, this seems pretty normal. He is in love with her, but he knows he shouldn't start a serious relationship with her until he's divorced his wife.
So, although of course he shouldn't have gotten involved with another girl at all while being married, this simply shows that at least he has the conscience not to go so far as to sleep with her as long as he shouldn't. So maybe he's not as much a jerk as you think.
Or is there something else, which you're not telling us?
