My son hasn’t left the house in months.
Well done for pushing on this, but my heart breaks with this line.
As a parent I'm hoping I help my kids to be the best people they can be, enjoy great experiences and learn from the bad. Its soul destroying when it feels like something outside of your control tears all that down.
While my son hasn't experienced what yours has, he has had a really tough, emotionally challenging time that for a long time "trapped" him at home in his own head. I worried, a lot, that he wouldn't get through it but time helps (its a cliche for a reason) - as does getting good support for you (parents) and, when he's ready, for him.
It may mean little now but I do think in the long run he will recognise that you didn't back away from this fight and saw it through. Hopefully when you and he look back on a long life this is only one short blip, and trust me I know it doesn't feel like a blip now.
Small steps, good support, new targets. By new targets I mean you have to let go of all the what ifs - if this hadn't happened, he'd be doing so well, he'd be out, socialising etc. Look for small wins for both him and you, because you have both been through hell - but its does get better.