I'm gonna use Loki and Thor for my examples in my explanation of what I think you could do to get what you want out of the situation. (Spoilers if you haven't seen any Avengers movies.)
Thor is our "good" guy, Loki is THE quintessential "bad" boy that all the girls scream over. Here's what you're facing up against:
1) Taking away the fact that he betrays everyone over and over and OVER, Loki has a LOT of appealing characteristics. He's witty, sarcastic, defiant, driven, and complex. These are all neutral character elements, and the combination of all five makes for a FANTASTIC character to follow along with. People have even pointed out that Tom Hiddleston, the actor, isn't nearly as 'conventionally' attractive as Chris Hemsworth, but he still outshines his co-actor in THOR movies because of who he plays. Not only that, but there's room for growth. When you pair a guy who has a lot of good things about him with the potential to be so much better than he is, potential to have that "I dun wrong, and I'm gonna make it better" moment - people love a redemption arc. Bad boys are pre-packaged to hit a lot of sweet spots.
2) Thor was...let's admit it, just a liiiiiiittle bit boring. I say was - when did it change? (Not Dark World, bleh...) It was in Ragnarok. When he became truly funny (adding to his depth of character), and when he was ACTUALLY brought low and had some serious things to face. They tried to humble him in the first movie, it sorta worked, but Ragnarok REALLY made Thor have to go through some stuff. Now, admittedly, Thor always had a little bit of bad boy in him because of his defiance, but he was still the golden child. The obvious protagonist. I came to like him much more as a character than Loki (and I LOVE me some good villains) when he became less of a protagonist and more of just a person. Someone who was good but who was genuinely and relatably flawed. Someone who was trying their best but who had potential and a LOT of room to grow - just like Loki did.
So the answer? I would suggest not changing your bad boy and reexamining your good boy. Is he TOO good? Does he have enough flaws? Maybe there can be more opportunities to put the guys head-to-head, not for the girl, but for the sake of their values? Do that, and you have two guys who are both fighting for something, the battlefield is level, and the audience has to root for one or the other. When Thor and Loki butt heads, of course people want Loki to get some vindication, but ultimately we want Thor to win. It's even better when THOR wants that same vindication for Loki, too, but just can't give it to him.
That's my drawn-out brain dump. Hopefully it provides something to think about! 