My sister hates my girlfriend, what should I do?

ScottSummers

Hello.
Ok my sister and me we were always best friends and we were always doing everything together so staying close with her is very important to me.
We moved out from our parents several years ago and we live together. Iam dating my girlfriend for over a year now and she often hangs out at my sisters and my place. Things were just fine at the beginning, we were all together watching movies or going out doing pretty much everything together. When i got in a relationship with my now girlfriend my sisters behavior changed towards her drastically.

Now she absolutely hates my girlfriend for some reason i dont und. My girlfriend is really always nice to her and she really tries to be her friend but my sister is always mean to her. Also she always talks bad about her when she is not around as well.
Sometimes she fights with me as well saying my girlfriend doesn't deserves me blah blah and she is accusing me of not being around anymore, of changing into a totally different person. I dont think thats true.

I really love my girlfriend she is just amazing in every way so breaking up with her is out of question also i know my girlfriend won't give up on me neither so i just feel bad because my sister is kinda suffering and she is sad most of the time cos of this.
My sister never had a boyfriend and she only has few friends and she doesn't even seem close with them.
Maybe she feels lonely and neglected by me so she acts jealous? What should i do?

Iam 22, my sister is 19 and my girlfriend is 18 yo if that matters.
My sister hates my girlfriend, what should I do?
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