MY GIRLFRIEND gets crazy for her friends instead of me!

Hi my name is Ankit.i have a girlfriend and we are in relationship since 8 years. There has been many ups and downs but we have never broke up but the problem which I m facing is this that she gets more happy when she sees her friends (females). I am not scared of losing her but her friends are not worth for her that is what I want to convince her. Whenever she goes out with her friends,they make her drink and smoke hukkas. My girlfriend used to drink earlier but she left when she came into relationship with me, but from past one year she is again repeating her past and when I try to stop her she says that m torturing her. I don't let her live her own life. I don't want to be a jackals in her life but the thing is I want to marry her and I can't take her home if she doesn't changes her drinking ha bit as my parents won't allow her in this behaviour. I am upset to see her going out with her friends as she gives them more priorities than me. They drink occasionally but still they talk behind her back that my girlfriend is not a marriage material. I don't know y is she so negative. Always say as that I m not sure whether my dad will approve u or not. First she tortured me for job, now with God's grace am having a nice job, still she is not sure whether her dad will approve me or not as she is sindhi and m agarwal. Please help me guys in solving this issue as I love her a lot.