I don't think it's jealousy towards MC. Given what happened a few hours earlier with Micha I think Rusty realises at that precise moment that he didn't just screw up the possible affair with Micha but also the date he had with Jill a couple of years before. He really realises what happened with those two girls was his own fault and if he really wants to start a serious relationship he will have to change the way he behaves.I Doubt Jill slept with rusty knowing Jill she would probably embarrassed if the guy she slept before and the new boyfriend meet. Maybe rusty was just jealous on fuckface because Jill dump even though he is the president of the diks and a burgermister.
I admit, however, that this is just a hypothesis....