I was going to post a harsh reply but this broke my heart.

Above all else, your son feels betrayed. You gave your stepdaughter the benefit of the doubt over your own son & if his mother isn't in the picture anymore you're really the only person in the world he can rely on to give him the benefit of the doubt. If you don't even believe him, then who else will? He feels betrayed by the one person who was supposed to protect him & believe him regardless of what happens.

He wasn't presumed innocent either, without any extra evidence provided (she couldn't have, there wasn't any) you still "decided" that you needed to turn him in. It was a hard decision & it took you a few days to do it, but that's a "decision" you came up with on your own. You decided to presume he was guilty instead of innocent, and you didn't even need any evidence to persuade you.

It will without a doubt take at least a few years to earn his trust & respect back, if he even decides to give you a 2nd chance. But don't push him, just give him the support he needs & let time do its thing.

If your son is actually reading this - buddy, give your dad a 2nd chance. Doesn't have to be today, doesn't have to be tomorrow, does't even need to be this year. You take whatever time you need but you need to eventually forgive him & let him make amends. He knows he done goofd, he made a shit decision and I guarantee you it's a mistake he will not repeat again for the rest of his life, nor will he ever forgive himself for it. Take it from someone who's recently lost their father, it's easy to stay mad at someone & hold a grudge while they're alive but you can't make amends with a dead man. At that point it's just too late & you're only left with a whole lot of regret to fill that hole in your heart. Take whatever time you need, but you gotta make peace. You're always gonna need your father.