I wonder if this pattern is sort of common. I used to have a similar cycle:

1. Date a bad boy, someone who didn't treat me well but who was very exciting to be around.
2. Relationship ends. Decide I was sick of dating bad boys and that I wanted to date someone nice for a change.
3. Realize that the person I thought was nice was actually not so nice or incredibly boring.
4. Go back to step 1.

It didn't work out quite as pat as that, but you get the idea. I broke the cycle by not dating ANYONE for a year. I made a list of deal breakers and stuck to it.

I used to think that I didn't like dating the 'nice' guys because there was something wrong with me, like I didn't want to be treated well, but that was not the case. When I really examined those relationships, those people were often just as bad as the not nice guys, but they expressed it in different ways.

If your instinct is telling you that you shouldn't be with this new guy, I'd spend some more time with that. Can you identify what triggers those feelings? I would be really hesitant to assume it is because you still have feelings for your ex. That could be part of it, but there could be another piece.

As for your ex, not talking to him at all for a good six months may finally let you kill off whatever feelings remain. He doesn't even sound worthy of your friendship.

It's really hard when you rationally know that someone isn't good for you but emotionally can't stop from reaching out to them. I hope it works out for you!