(bisexual) why after breaking up with her i feel like i love her even more?

okay this is whats going on IM A GIRL and i dated guys alot before i meet my current girlfriend, its been 2 year now and since the beginning i was not sure weather it was right and always broke up with her ....but the deal here is that when im with her i always start thinking that same sex relationship is not right we are sexually active since the start and when i tell her i don't wanna be with her anymore she tells me that she loves me and that as hard as it is for her shes gonna let me go for good now and that shes really tired of the way im acting with her....i know she loves me i could feel it she shows it to me in every way and shes been there 4 me to ...but what i don't understand is that why every time we break up i feel different i wanna be with her i look for her and tell her how much i miss her and that i love her ....she trys to be strong but then i tease her until she comes to me again and feel like i love her we act like we are together again but then after a couple of days i start thinking the same thing again and she always tells me that its not fair how im taking advantage just cuz i know how she Truly feels for me .

PLEASE HELP I DONT KNOW WHY IM THIS WAY WITH HER
if shes one of those girls that's romantic caring faithful makes me feel important shes a one of a kind honestly