Most Helpful Girl
Sweety, you cannot win every fight and not every fight is worth fighting.
Being on and off for 6 years, him being with other women in between and coming back to you whenever and you taking him back every time is a vicious circle. you are selling yourself dramatically under value and are showing a big lack of respect for your own well-being.
A relationship should be fun, it should make you happy, it should be the place you can come home to and be safe when the world is crappy. Of course there will be bad times, but the good times should outweigh them.
What do you want for your future? do you see it happening with him?
Only you can know if there is hope for you two. Couples therapy will be useful, maybe a joined session with his phsychiatrist. He needs to commit 100% for any chance of this working out.
Just never forget that you are allowed to move on without him, you do not have to feel bad for doing so nor like you are abandoning him. It is after all your life and you have the right to be happy.