Stop running back to him.
In an ideal world, we would all have someone to save us. Someone who's always there to give us a hug and tell us everything is okay. Someone who can pick up the pieces of our broken hearts and put us back together.
But in reality, that person does not exist.
We're all selfish creatures, and there's no way we can expect that kind of loyalty and dedication from someone. And if you do find yourself with someone who wants to "fix you," it's probably not for the self-sacrificing reasons he might want you to believe.
It's a selfish tool that's only meant to manipulate you.
Because when you start to rely on someone for that intense emotional support and self-esteem boost, you need them. You become dependent on them for your happiness — making it that much harder to leave the toxic relationship.
A guy who constantly tears you down just to build you back up later is doing so for exactly that reason. He keeps you weak and hurt so you don't feel like you can live without him. He feeds off the power and control, which is why you have to stop giving it to him.
That kind of relationship is toxic, abusive and will only break you further. You need to get out. Immediately.
You're the only person who can save yourself.
You're the only person who can put you back together.
You're the only person who should build yourself back up.
Relying on somebody else for your happiness is the quickest way to lose it. The guy you're with shouldn't want to "fix you," but love you just the way you are. Because there's nothing wrong with who you are, right now.
If you find yourself in a relationship with a guy who claims to be a saint but only makes you feel like shit, then do yourself a favor and leave. It will hurt. You will feel like you don't know where to go or what to do, but you have to start somewhere.
You have to learn how to save yourself.