If your girlfriend/boyfriend is in love with your brother/sister

well,if it happens around me,i will know the thing exactly.if my girlfriend gets the first step to him,i'll abandon her and try to persuade my brother to do so because i know what is she.never talk with her from then on.and if my brother get the first step to her,i'll hit him ruthlessly and consider everything didn't happen before.and i'll be myself from then on.

Asking the sibling to forget him/her may not be a good idea because they may be deeply in love with each other. It may strain or break your relationdhip with your sibling. It may bring them even closer together.

A sacrifice may need to be done here. Let the sibling take the girl/boy. Find something else to do so as to keep the person from intruding into the mind. There is always someone else better out there.

all the best,
rosdimy

Well, you cant force a person to love you if she/he doesn't.

The important thing here is to find out whether he/she is a responsible person?
Clear the follwing doubts; Why did he/she go steady with you in the first place?
Is he/she still unsure? It is going to be awkward and irresponsible if he/she love either one of you at different timing.The best solution is to end the relationship and also warn your bro/sis about it. this person may not be worth loving, it implicates your family ties.

However, if he/she is serious about your bro/sis and your bro/sis also feel the same way, then perhap you are just a mistake. this case is very rare.
so do note to clarify.

I am very broadminded ...
However, I expect my G/f to be close to me only ... Not to my brother or cousins or anyone else!