I try to make everyone happy while im suffering inside.

i'm a 28 year old guy. i was born and raised in india and i live with my parents and 2 sisters. i have been in love with a girl for the past 7 years. we started dating in college, after 2 years passed, one of my sisters came to the same college as well, things were great, my sister liked my girl friend and everything was just perfect. after the second year, my girlfriend transfered to another college. she was doing her pre med so classes were extremely hard and phone calls were just at night time as i had to study as well. slowly the phone conversations between my sister and my girlfriend also started to go down. thats when all hell broke lose. my sister would accuse my girlfriend saying that once she left the old college and went to the new one, she changed. "i bet she thinks she is all that".
i tried to convince my sister saying that my girlfriend did not change and she is just as she was before. thats when my sister pointed the finger at me saying that i have changed too and that i never believe my sister and always taking sides with my girlfriend. i wasnt the perfect guy to begin with, and i am honestly proud to say that my girlfriend changed me into a more responsible and independent person. and my sister just cant stand it.

i'm the kind of guy that wants everything and everyone to go in peace and harmony. but with my sister acting all crazy like this, its not happening. one day my sister and girlfriend got into an argument for something reallllllly silly and my sister said so many things she was not supposed to say.

and ever since that, my sister has been treating me really bad. she really hates my girlfriend, and there hasnt been a single day that passed without me praying that things would get at least a little better between them. but no. and i dont know why i desperately seek the approval of my sister so bad. she would say reallly worse things to me, stuff that you should not tell your brother, or anyone with a heart.

if i do marry my girlfriend and bring her into the family, i know for a fact that my sister is going to give her the cold shoulder and will definitely talk behind our back.
and i just found out recently that my sister called my grandmother and said all kinds of bad things about my girlfriend.

all this is eating me from inside. i have to have that "i dont care" attitude, but it just cant. i want everything and everyone to be peaceful and happy.

what should i do? help me. please give me some advice.

thank you so much for responding, i feel so much better.

shuvvykins, its like my sister is tryign to brainwash everyone in the family saying that all my girlfriend is going to bring is misery and hatred. she said it so many times that, even my parents are going to look at it in that way. its like the saying, you see what you want to see. if you look at a person thinking they are crazy or bad, each and everything they do will be crazy and bad.

but thank you guys, from the bottom of my heart. i really really appreciate you taking the time to respond to my dilemma.