is it okay to have a BF/GF immediately after a longtime relationship??

I think its ok, as long as ur sister has moved on, u didnt say wether she dumped him or if it was a mutual decision or nething, so depending on the circumstance it culd be. I dated someone for a year, we broke up, and i was amazed to find two weeks later i was with someone again, so it does happen i guess,

Well.. I think it is not okay to have another relationship after a longtime relationship.. it is because the feeling might be because you are not used to being single and you just want someone by your side.. it is not fair for the other one who has feelings for you.. You may also tend to compare with the last relationship.. it is best to get to know the new person more before starting another relationship.. you will onli cause pain to the person who likes you previously and i think it is not fair for the person too.. other pple who see you get involved in another relationship may see you as a flirt and may spread rumours about you.. so it is better to be alone for a period of time and set your priority first before moving on with another relationship..

I think that's OK but they're called rebound relatiohships and from what I've heard, usually don't last. But I also think that it's important for anyone to give themselves time to heal after getting out of a long term relationship.

it depends on how long does it takes you to move on. :D