Training obsession

I am stepdad to an 18 year old aspie. I married his mum 10 years ago and we spent many years doing things together and had a good relationship. He was sporty, ran in a local half marathon and did boxing. During Lockdown, he couldn't train at the boxing gym, so he started training in his bedroom and the garden.  His routine has taken over his life as he has been training for up to 12 hours sometimes. He has a fixed routine and also runs nearly every day and I can see that he is getting thinner and thinner. He will miss family events and college instead of missing his training and he as become an angry, distant and irritable person, who to be honest is a nightmare to live with.  He also refuses to wear clothes most of the day, wandering around in his underwear.  When I try to speak to him about anything, he walks away and gets angry. if I ask him to do anything such as tidy his own room and bring down all the plates, cups, glasses, cutlery and rubbish that he accumulates. Also there are the usual piles of dirty clothing mixed up with the clean stuff.   His mother thinks that I am responsible for some of his traits and often blames me for not doing enough, but he refuses to communicate with me and won't see sense.  This all started on Christmas day 2022 when his cousin who is also his uncle and his brother, stayed with us and they both decided to sneak downstairs and open all their presents during the night. For some reason, they both decided to blame me for spoiling Christmas and proceeded to tell other family members that they hated me. Its not been the same this then and its actually tearing apart my marriage and the fact is, he does nothing positive or helpful or  any acts of kindness in our house anymore. I don't know what to do.