I hate the extra person in our duo because he makes me feel like a third wheel.

So basically, I have a friend and we have known each other for 8 years. We became best friend 4 years ago and we really enjoyed each other's company. But then this third person enters our life, I hated him from the start, He was like the "gang" leader and everyone would do his bidding. So naturally me and my friend hated him because he was so manipulative but recently I got sick and I didn't attended school for few days and even if I did, I rarely even talked to my best friend. I think he felt that I was not interesting anymore. So he started talking to the manipulative guy. And they got along so well, I haven't recovered yet so I still doesn't bother to start any conversation but I am noticing that my best friend is getting distant from me. He would rarely talk to me but he will always strike a conversation with the manipulative guy. I feel like even if I recovered it will be too late. I feel like I am becoming boring to others, day by day. This is making me feel like a third wheel and decreasing my confidence, Now my best friend hang out with the manipulative guy and I feel very jealous about it, Help me out here please.