why does my sister continue to want to have $ex when she has STD. I also have it too because of her?

You had sex with your sister?

Or did you get it from close contact AKA sharing drinks?

Sex is part of the meaning of life. Why not ask a fish to stop swimming?

Ah.

She still has the right to have sex, as do you but she should inform her partners about the std if she still has it the next time she wants to have sex.
Unless you had sex with your sister you're not likely to have it. Stds are rarely passed out side of having sex.
I know it sucks to have an std but most of them can be treated with antibiotics. Herpes, HPV and HIV can't be cured but they can be managed with treatment and medication.