That sounds tough. I hope you're taking care of yourself.

People can change. Of course they can. Maybe the guy you're dating can too - but he has to want to change. No one can do it for him, it's got to come from inside him.

If he's acting supportive for a few days, then going back to his old self, it sounds like he doesn't want to change, and he's doing it to appease you. As if you'll forget about him neglecting you if he's a bit nicer for a spell, then he can get back to doing what he actually wants.

If he's telling you through his actions who he is, believe him. Don't put all your time, love and energy into someone who won't return it. You deserve better than that.