The yetzer hara is confusing you with guilty religious feelings. Don’t let him. You have to take care of yourself first. I’m going to be blunt: you sound like you are codependent on your husband (which is understandable), but you have to just let him go!
Try to fix the marriage. If it doen’t work, you have every right to divorce and find someone else. Your husband will have to get chizuk from other sources throughout his life and not be dependent on you for it. It is not your responsibility to change him or save his soul. Try it for the time being, but if therapy doesn’t work, then take care of YOU first. I would also suggest going to therapy now to work on becoming more emotionally independent.
If you really want to know halachik advice on how someone who may be a shoteh gives a get, speak to a Rabbi. As for your marriage, Hashem wants you to be happy first and foremost.
I’m sorry you are married to such a dishonest loser.
Be strong!