I read this manga long time ago, it's about a high school boy and he's the leader of a gang. He's strong and well-known, but one day a strong gang crush his gang, and he's fu*ked by that gang leader. Since that day, the gang leader fall in love with him..

If I remember correctly, he has a friend, for some reasons I stop reading this manga so I dont know if it ended or not

ummm do you mean gang?

Maybe Steal Moon?
I haven't read it, but using some keywords
I found Aoi Hitsuji no Yume, Steal Moon being its prequel.

Hrodulf and Bjornolfr, you will not be forgotten.
[img]http://i411.photobucket.com/albums/pp199/SyberAngelGabrielle/couplesig.jpg[/img]
[color=black]And if the world were black and white,
you would be my rainbow in shades of grey.[/color]

Click 'n Play!

If I had a fantasy self, it'd be a tentacle monster.

Steal moon series is nowhere close to it 🤣
I think one of the stories from Tour Shangri-La is preety close, with the bike gang and getting fucked when he lose.

Oops Im sorry, yes it's "gang". I've checked your suggestions but none of them is the manga I read 🙁 because Im not sure I finish reading it or not so maybe it's hard to find this manga depend on summary 🙁 I guess..