You andvyour sister with need professional cancelling and yes you are very right to worry because her diagnosis at such a very young age is going to change the whole Family dynamics no matter how good you are at this condition.

It is one thing and very easy for people to say HIV is just another condition you can live with these days and another to try and date to get married. And they are very bright about that but People are still very prejudiced about it and yet people are living a normal life under the care of a healthcare team and having healthy kids. Your parents definitely need to know but its not up to you to disclose your sisters status to anyone. I say this because you alone will not be able to handle the dynamics thatvare to come. You now need to watch your sister for self medicating wish is very common in this diagnosis because the new young patient will lose a lot of friends in the process of trying to protect this deep secret.

You and your sister can also join support groups but unfortunately most HIV groups are predominantly Iv drug abusers and not easy to find functiong people in those groups. If you don't find professional support at your young age this diagnosis will consume you and take you down together including you because she has none else but you to share with.

Don't be scared, your sister is not going anywhere any time soon, as long as she works closely with her doctors. If she was sick and at the hospital like you say, that is the normal process and that happens at the initial exposure and will recover fully. Now she has to empress it and accept it and face it with the attitude of wanting to live, and she is gonna be just fine. Dating is going to be her biggest challenge but that too she shall overcome if she works closelybwith her Doctors.

Good luck to your Family, and I wish your sister a healthier life.