Im only 15 and i feel lonely almost everyday i guess

I have some friends but its not like im in a group or something. They already have their own groups of friends so im just like a person to talk with when they're in a same class with me. I have like one or two really close friends. But the problem is when i see a group of people hanging out together i feel so left out. And not part of the society or something. Even when my friend is right next to me. I dont own any social website accounts and i have tried every single of them but they were too addicting so i deleted them all. So i feel more lonely but i dont want to start on those.

How do you feel less left out and lonely?? Make more friends or chat with strangers wont help.. ive tried everything already.

HELLPPPP