You might want to examine the first chapter and consider how Bryon presents himself in this opening section of the novel. The first paragraph tells us that Bryon is very good at pool, he is sixteen, and he is a "baby-faced kid who wouldn't know one ball from another." The fact that they are here to "hustle" and that they do this frequently indicates that Bryon has a rather unscrupulous character, as he is not above breaking laws to enrich himself. Also, note the following description that Bryon gives about himself:
I'm a big guy, dark hair and eyes--the kind who looks like a Saint Bernard puppy, which I don't mind as most chicks cannot resist a Saint Bernard puppy.
Bryon also clearly sees himself therefore as a bit of a player who has had many girlfriends in the past. The way that he and Mark save M&M from being beaten up and the matter-of-fact way in which he fights shows that he is no stranger to violence, and lastly his relationship with Mark demonstrates that he is capable of deep affection and love. You might like to analyse other sections of the book now that I have started you off and see what other traits of Bryon emerge.