Thats a really good question..... before I started dating my boyfriend, Brad... he lived that single life. Going to the bars all the time, going to see strippers, drinking with his buddies at his apartment, golfing, doing whatever he wanted, whenever he wanted.
And then he met me, he changed his ways completely. And that's not even a slight exaggeration. He went to the bar a couple of times, had buddies over to our apartment to drink, watch movies, whatever... and that's definitely okay... he had a crazy lifestyle before, what's going to the bar a couple times ? ... but he changed for me. He hasnt gone to the strippers since we started dating, he said he never really enjoyed it... he doesnt do any of the stuff he did before. Now hes into having a family, he got us a puppy... the whole bit.
I believe they can change if they're REALLY willing. But be careful... he could be saying that because he wants you to stay, because he's so used to having you there, letting him do whatever he wants, but still having you. He may not mean he actually wants to change. Let him prove it before you go back to him....
Good luck and keep us posted!