How to keep a relationship healthy?

I dont understand what to do , i used to think if i treat my gf very well, if i love her very much , keep her happy , care about her feelings and emotions , never let her feel alone , always prioritize her always keep her above everything , then she will always love me and never leave me and we will have a perfect relationship

but everything i thought was totally fake , everything backfired
she begin to take me for granted like crazy , stop valuing me , stopped taking interest in me , started to found me boring , irritating , she became totally heartless towards me and said me all kind of stuff without any regret or anything , and told me that she cant stay with me because i m too nice and she doesnt feel any fear guilt or regret whenever she does smtg bad to me , and thats why she always remains pissed of from me for no reason and cant live with me

i used to cry alot i used to tell her how much it hurts me , still i used to go back and i used to think that she knows that i m hurt and i still came back , so now she will sympathize would start treating me well , but no the bad behvr just kept increasing exponentially

and now i m just left confused and numb that what i did was just love and love and love and still i got this terrible treatment? like why? what do i hv to do?

i used to do everything for her , for 1 year i left everything for her didnt make new friends in our new coaching and in the 2nd year when she made friends and i was alone , she didnt care about me she didnt think that i am alone and she shud be with me , but in the prvs year i was with her always , i was an extrovert i cud make friends back then but i couldnt see her sitting standing alone i used to be with her , but when she made friend she never cared if i was sitting alone in some corner of the class or standing alone outside the coaching waiting for van

when she was bored with her friends , and wanted to get out she used to call me only then
and when she was taking interest with her friends she didnt give a fuck about me

this is not even the tip of iceberg , and i m being serious so many things have happened u cant even imagine

vo hmesha hurt krke mujhe aise hi chordh deti thi kabhi kuch solve nhi kiya , hmesha main hi hurt hhota tha main hi rota tha uske liye , fir main hi aakar uuse beg krta tha vapas aane ke liye
and ye sab 2 saal mein pta nhi kitni baar hua har week 2 baar atleast , and usne kabhi nhi socha kitna 2 saal mein accumulate ho gya tha mere andar use lagta tha raat gyi baat gyi , but aisa nhi hota h
ye kuch bhi nhi h ptani kitne incidents h kitne to yaad bhi nhi h mujhe sab incident mein main hurt hua bhot zyada maine hi bheek mangi , usne kabhi nhi manaya mujhe usne starting me hi boldiya tha relo ke ki vo kabhi manyegi vagereh nhi kyuki use ata nhi , main incidents btane chala to itne khatarnak h sare and sab jab ek dusre ke upar accumulate hote h to hurt or bhi exponentially zyada hota h , khatm ho jata h mentally insaan , just imagine u cut ur hand with a knife then put salt over it then hot water then again cut it and keep repeating it endlessly

like what was this why this happened with me? is loving someone this much bad like what to do everything is ruined