Why are you being so hard on yourself? You deserve to be happy.
It's a dirty trick that unfortunately isn't that uncommon, when the cheating partner turns around and tries to make you feel guilty about what happened. I'm talking about him calling you unsupportive when it's he who's being unsupportive.
This very well could be just a "bump" you need to fix, but that requires him being on board with fixing it. Right now, it sounds like what you need from him to fix this relationship, is to let go of this guy he cheated on you with, or at least put it on hold until your relationship is solid again. If he's not even willing to entertain that idea, then he's not interested in you and the relationship, but only in himself.
I agree that it takes years to really get to know someone... but only a couple months to realize that you can't stand them
Basically, as soon as the "honeymoon phase" wears off (on here, we call it NRE or New Relationship Energy), you start to see someone for who they really are. Then you decide in a matter of days or weeks that you like who they really are, or else you move on.
Now, I'm not saying it's impossible to meet someone in high school, marry them, and live happily ever after. But it's not at all common, and most people who try are really just afraid to be alone and settling for less than they deserve.
The way I see it, in every happy & healthy relationship, the good should outweigh the bad. The bad should be things that you're both trying to work on improving and eventually eliminating, where possible. By your description, it sounds like the bad outweighs the good. Staying with that is selling yourself short.
Hon, it sounds like he's using you. He knows you have low self-esteem and that you're not going to stand up for yourself, so he's just doing whatever the fuck he wants, regardless of how you feel. That shit just ain't right!
That leads to my other concern: Do you think you're healthy and happy enough right now that you would have something positive to bring to the other couple? Or are you just looking to escape your current situation, and hoping that they'll swoop in and save you? It's not fair to them to put that kind of expectation in their lap. Only you have the ability to make yourself happy, no one else can do it for you. And until you make yourself happy, you can't be part of a happy, healthy relationship.