Fabian lives with his mother.
He considered Jeremy his little brother, although he wasn't.
Fabian is best friends to Niklas and Jason.
Fabian is more introverted than Jason. He plays guitar and he likes to be on his own sometimes. And he is stubborn.
Fabi lives alone with his mother. There were times where his mom had a friend who had a child. And they all lived together so that Fabian had a "sister" or a "brother". But his mom never married again, and when her friendship was over, the man and his child left. This happened one year ago for the last time. Fabian called the kid, Jeremy, his "brother", and he was sure that this time they would stay. That his mom would marry. But one day Jeremy and his father were gone. And Fabi was very hurt.
The agreement with Jason and Niklas was his idea. He probably doesn't want to loose a friend anymore.