That all depends on him, days, months, even years. I myself wasn’t so on the derech growing up. I was a very confused teenager and it took me until I was about 20 to get myself into gear. Baruch Hashem I had a wonderful relationship with my parents even though I was not doing as they wished they decided to support me all the way. There is no sitting shiva for a child who goes off the D.
Sometimes people like your son just need to feel accepted. It’s always better if he can have someone to talk to if not just be the supportive parent which sounds like you have been. Never lose hope in him.
Since there are over 2000 posts on this thread reading it all is just too much so I do not know if any of this was said.
Like all children or adults whom go off the D they are part of klal yisrael and no matter what they do they still need our love and support. We need everyone to bring this long galus to an end, we should adopt the policy leave no one behind.
Much Hatzlocha!!!