Why on Earth was your stepdaughter was so afraid of you learning she was having sex with boyfriend? Was she afraid of your or your wife? How would you find out unless she got a pregnancy scare?
And I am sorry, I have tried to find nice or supportive words for you, but I cannot. Yes, you tried to do what is right after you learned of a heinous crime. Yes, you did the most of you could to fix the things by disowning the stepdaughter and promising to repair all the damaged things.
But why did your stepdaughter need to lie at all? Why were you so ready to trust her over your biological child who you should have known better and longer, with him having lived with you and being of the same gender as you? Speaking as a psychologist - this is extremely unusual to others and extremely toxic to him.
And speaking from experience - your son will hate you and your wife for the rest of the life. Period. He'll hate you with burning passion even when he is ninety and you are long dead. Time will not help things much as passage of time will only remind him of how long the stepdaughter passes by with her being unpunished (unfortunately, disowning her will not make him feel that she got what she deserved since people will tend to believe it is not her own fault).
The fact he has to live in the same building as you is painful enough. At best he won't even want to hear you exist for years, possibly ever. Forget about talking or emails. He'll never forgive but at some point in the future he might find strength to at least communicate with you - that depends mainly on how you treated him before and if he manages to regain enough control of his life.
He is now in mindset where he wants three things: 1) this to have never happened (undo) 2) having the stepdaughter's life ruined permanently and 3) moving as far as away from anyone involved for foreseeable time.
1) is not possible obviously, 2) is not happening as disinheriting and disowning her will not feel as appropriate punishment by him who is now basically considered to be a sex offender, and she won't be prosecuted. The best you can do is 3.
One poster mentioned that the best thing to do is give him his inheritance early and help him to move to another place. Preferably, another family member or friend should from now on serve as a person to check up on him and support him emotionally.
Don't push for contact or communication as it will be counterproductive - if he is ready at some point in the future to reestablish communication he will do so only of his own volition and not because you are persistent.
He should also continue with therapy as he probably has non-insignificant suicidal risk (also speaking from experience).