
Ahhh, ngl... I hate those kind of backstories. I understand if the character had trust and mental issues but there is no reason to be homophobic. One person doesn't represent an entire community.
Then again, it could be internalized homophobia. For ex: He was molested by a man at a young age and he believes thats why he likes men.

Actually unfortunately that's not very uncommon
Gay kids who have been molested before have a harder time to accept their sexuality because for a long time they had that person as a sick and bad representation in their mind
And by being gay it makes them think they are like that too
But that happens usually when they are in middle or high school when they still dont know many things and cant differentiate between someone actions
We still dont know but I think he really fits to this
Considering his strong reaction when he was kissed in high school and his way more mature reaction to his brother coming out
But he hasn't accepted himself yet and he still wants to fit to his ''cool boy best boy" image so that's why he is that way

Yes, I know... it's so sad. A few of my LGBTQ+ friends have talked to me about struggling to come to terms with their sexuality due to being sexually assaulted at a young age by the same gender. It never made them homophobic towards others though, more towards themselves.
They were unable to love and accept themselves for who they are. After years, they now do. I hope the same happens for him, regardless of the backstory.
And here we go for the child molester arch