Michael was unfortunately a victim of childhood neglect, mainly from his father. His father was not a good person - especially to his other. Lucy is an ex-hippie, meaning her husband/Michael's father most likely was as well and it's also an unfortunate fact that abuse was pretty common in a lot of that subculture. I do not believe Michael, himself, was ever physically harmed as I believe if such an incident ever occurred, Lucy would have put an immediate stop to it. I do believe, however, that his father didn't actually care that much about Michael and cheated on Lucy for most of their marriage.
Michael's feelings of neglect grew even stronger after Sam was born, however. Lucy needed to make up the love, care, and attention of two parents while also dealing with her own complicated feelings on her marriage. Michael felt as if Sam was the favorite and felt even further ignored by his parents as his mother dealt with a new baby and his father continued to be absent. Michael does not blame Sam for this, however, nor does he currently hold any resentment. Most of Michael's issues are related to his parents.
Michael really tried to earn his father's approval, however, and a lot of his issues began to be internalized. He wanted to be a good kid. he was quiet, decent enough, and more mature for his age than he needed to be. He also began to grow more and more independent as his mother was more focused on raising a younger child while Michael was already a few years older. All of this is the reason Michael is quiet and low-key and low energy. He feels as if he needed to be reserved in order to be a good kid.
This desire to be a 'good kid' and his restrained personality is part of the reason for his hobbies. he preferred engaging in hobbies he could do by himself, such as building model cars or getting into automobile mechanics. This is also part of the reason Michael joined baseball. Michael likes sports and he likes being active and he thought joining a baseball team might be enough of an incentive for his father to come to his games. Especially if he played well. Lucy tried her hardest, but Michael's father never really bothered to attend his games on more than a handful of occasions. Michael stopped playing baseball before high school when he realized it wouldn't matter.
Michael has a need for acceptance, which is part of the reason he falls so quickly in with the Lost Boys. After a childhood of neglect and a massive move after a messy divorce, Michael is left reeling and falls in with the first group that seems to want and accept him. The Lost Boys also bring out parts of Michael he'd subdued for so long, such as some of his reckless and bold nature. Michael liked hanging around with them and, for a moment, genuinely felt that 'freedom' they sort of embody.
After the Lost Boys basically scared the shit out of Michael by eating those surfers, Michael sort of put up this mental block between them and immediately disengaged from them. They were heartless monsters, they didn't care about anything or anyone. They were irresponsible, childish, and nothing but killers. It was easier to pretend he didn't feel connected/free with them and easier to pretend any good traits were just lies. Or nonexistent. To Michael, they're heartless monsters, when it's proven they genuinely do care about one another. He also sees them as irresponsible and childish, despite them knowing themselves better than Michael really understands himself.
