<human>: Can you provide a brief rundown of the text in within 3 sentences?

I[19M] have been dating my GF[19F] for about 1.5 years now. I have kept her a secret from my family this entire time knowing that they would disapprove because she is Muslim and my family is Hindu. I couldn't take the pressure anymore so I caved in and told my parents.

My parents were incredibly upset and reacted far worse than I anticipated. They cannot stand the idea of my GF because of her religion. Both my parents broke down crying saying that they didn't expect this and that this is not what they wanted from me. Seeing them cry caused me to tear us as well.  

This is when they gave me the ultimatum.

They told me to to chose either them or her. 

I love her. I can't imagine my day without her. I don't want to give her up.

If I chose her my parents will pull out financial support from me. I can handle this I have been prepared for this. But what they added on was that they would take my sister [7F] and move back to India so that they can "at least hold on to her". I would never see her again if they can help it. I can't live like that. I want my sister to grow up with me around here in the US. Since we are all US citizens it would take some time before they moved back but they will do it.

I can't throw away my sister like that. I know that even though I have been with my GF fro 1.5 at my age the relationship has a significant chance to fail.

At the same time even if I chose my family I know that I can never live how they want and they will throw this ultimatum again in a few years when I find a girl that isn't to their liking.

I have no idea what to do and I need to give an answer by Thursday(Feb 6).

I cannot straight up chose her. But I am contemplating continuing our relationship in secret. But if my parents found out they would pull out just as they promised.
<bot>: My parents gave me an ultimatum. GF of 1.5 years or family. I am lost as to what to do.