Does a tiger ever change his stripes?

Here's the situation. My fiancee and I are in different countries, we'll just say that. Met on vacation, and I have been back twice to see him. On the second visit, I stumbled upon his emails (I didn't do it intentionally!) and it was all these matches from dating sites. At this point, I was already wearing an engagement right. So i was suspicious, because of the long distance. So I searched his username on a dating site and found him. His account was created before we met, but he had added photos that I took of him a few days after our engagement! I was shocked. Needless to say, I think he has a problem with trolling online for women. i know this is what destroyed his first marriage, he admitted it. Anways, I confronted him on it and he seemed sad, but defensive at first denying that he was doing it lately and i told him about the recent pics and he was apologetic. So we have been argumentative lately - just about nothing in particular - so i decided to google his username, and found his name on another site. AGAIN - created before, but logged in last...the day after I left from my last trip, when i threatened to leave him if i ever found out he was cheating on me. Its really eating at me. For me, this is going to be a big move to say the least. Do you think he will change? Do you think I should bail? any advice of any sort would be appreciated, although sometimes I think I already know the answer. He has deleted the accounts that I knew of, but I think I will always be looking over his shoulder at his phone or his computer thinking, what is he doing?