Should I have a grudge?

Stop living in the past. This boy didn't like you, but he likes your sister. It happens. It's you that is causing the problem. Your sister is doing nothing wrong (with the exception of having low morals.)

Since that guy never pays u any attention; i suggests u got to move on & find a better guy to love u ! Never hold grudge against anybody bcoz what goes around ;comes around back at u !

I would let her know that I was upset. Hardcore upset. I'd tell that I used to have a huge thing for him and for her to simply just have sex with someone you had such a strong feeling for. But if you want to let it go, and let her realize that she doesn't effect how you are in life. Even if she does, give her a smile that lets her know that you are stronger than her..

Move on or take him away from her.