Modern MurderMedia anon back to answer questions~

Alastor had an existing attraction to Vincent. Started as hate because how dare his already shitty father remarry after his perfect wonderful irreplaceable mother passed, but then this scumbag has the audacity to have another kid with his new wife!? He hated Vincent for awhile, but Vincent was imprinted on his older half brother. It was when Alastor was a teenager, he realized he can mold Vincent into the perfect puppy for him, but because of social norms, he kept the fantasies he'd have to himself not knowing Vincent was also secretly masturbating to the thought of fucking his hot, mean older brother. Just imagine all those years of pent up desire they had and it taking Alastor having one too many drinks to allow him to relax and give into his feelings for the two of them to finally release them. And wildly in their dad's really nice expensive car.

After that, they agree not to speak of their relationship to anyone, but the secrecy makes it hotter. And both secretly fantasize about being caught too.