I have ZERO (0) experience with this, since I have been spilling emotions all over the place since day one, but I'll try to help! I mean, I was edgy in middle school, so maybe I have a little experience?
Here's what I do know about feeling emotionless: you feel deeply, horrifically empty. You have no sadness, sure, but also no joy. Like @Young-Dusty said, he can still carry on a social life and try to enter relationships with the people around him. But the fulfillment won't be there. He could go through the motions and do everything right, but he won't get excited when his friends text him. He won't get upset when someone hurts them.
After time with this, he's probably a good actor. Like I said–going through the motions.
Same thing happens with his mom. Sure, he can be the best son ever, make her relaxed and happy, but he won't feel anything after that happens. He just won't care. After all this, the emotions he can't express are going to get stir-crazy. He won't get angry, exactly (emotion alert!) but he sure will feel wrong. Deep down, on an instinctual level, he will know that something's missing.
Emotionally vacant characters tend to turn to outlets like recklessness and sometimes drug use for a sense of simulated elation (adrenaline highs and regular highs). I'd expect some of that from your character.
Those are my best attempts! It's hard to write someone EMOTIONLESS, since by definition, they'll never become said. Logically, being unable to feel/express joy is what drives someone into a depression. For your character, it'll just drive him to become jaded.