Toxic Relationships~How?Why?What?

Hi
I know I haven't posted in awhile and thats because Ive been trying to live my best life.  While doing so someone has come in and out of my life but this time I thought it could be different, this time i thought we could be friends.  To put this relationship into terms that people would understand I would say this person was my first love and my only at this point in my life.  Me and this person went on for two years talking almost every single day knowing everything there is to know about a person but things changed.  Things became toxic and we didnt realize it until it got to the point where it was over our heads. We got to a point where we couldn't communicate without it blowing up and him blocking me, we got to a point where our love for one anther was expressed in anger.  He would scream at me over the phone and tell me how much I annoyed him and how there was something very wrong with me all because i asked too many questions.  but he always came back, being his best self for two weeks and then slowly becoming who he actually is.  Ive loved this person for two years given him everything and when i look back i can see how much I lost.  I lost the idea of myself, the idea of how much I should mean to myself, I lost my life outside of him beaus I only wanted to be with him. I talk to so many people know that get angry at me for making these choices on thinking he's going to be the person I fell in love with so many don't understand, and I don't either.  But I do at the same time, toxic relationships aren't just with friends there with boyfriends and girlfriends too.  My boyfriend was not mentally stable and I understood that Is good by him through the countless things he would tell me and they scared me.
I guess to anyone who asks why get back together with someone that is so clearly not ok is because I want him to get better and I guess in someway I want to be there when he does.  I know in the end were not meant to be and he doesn't truly care about me and that makes me incredibly sad.
The reason Im writing this tonight is because I just got blocked on everything.  I don't know how to be ok with losing someone so much, and someone taking so much of you for granted.  I want o say he didn't get to me that he didn't ruin me but he did, he always does.  Ive never been to such a low point but he brought me there.  If your in a toxic relationship make the effort to get out make the effort to reelaixe your better than that, please.
no one is worth losing yourself over.