I just don't get it..

So I have a group of friends and well sometimes we appear close. However I feel like there are times where They don't really acknowledge my presence and instead choose my younger sister over me. I know it seems like jealousy and that I as an older brother am supposed to protect and be happy for her but sometimes I can't help but feel annoyed at the fact that my friends mostly ask for her and prefer her. Like today my 'friends' came to look for my sis because we didn't go to school and looked for her and not for me. They are happy to see her and act normal with me...and sometimes I can't help but feel both left out and sad. My sister claims I'm just imagining all the bad stuff but honestly I feel like if I weren't there no one would care. But if my sis weren't there everyone would literally freak out trying to find her. They give her stuff too and well I'm usually left with nothing.. I know it's like Jealousy but how else should I react? I just don't know if these people are really worth calling 'friends' anymore. Despite all the good times I shared with them I get the feeling deep down that maybe they interact with me because of my sis idk..And well yeah I'm just not sure whether to cut them off completely or to keep talking and hanging out with them. I tried ignoring them a few times to see if they noticed I wAs gone and it appears that they truly don't care if I'm there.. This has been bothering me for awhile and I'm in dire need of advice..what should I do? Should I not talk to them ever again? And if so what would be the best way to avoid and bid farewell to them..please help