Pla give me the name

Does someone know the name og that one where there is a main character trapped in a dungeon for several years cause his teammates betrayed him cause he was too strong. Then he came back out of the dungeon but he became his own constellation. I think it was a serpent or sum. He had a scar I think but it got removed and he got a hair cut so he looked hot. His last comrades sold all his shit too, so he went to the museum to get em back.
WHAT IS THE NAMEE