Teen mental health in lockdown

Hi I have a 16 year old son with Autism. He is high functioning and has managed to stay in main stream school. He was very stressed until recently about his up and coming GCSE's. When the government cancelling them and he knew he would most likely get the grades he needed for college, it took away that stress and anxiety for him. Sadly that has now been replaced with depression and self hate, due to both the coroner virus and problems with friends and a girl he chatted with online. I have tried to gently encourage him to have a goal of some kind and to point out the positives about himself, but this has not helped. He has also talked about harming himself when he is at his lowest. We are stuck in a flat which makes it worst. He is an only child with no siblings to interact with just me, his mother. He is too young to volunteer, and college seems a long way off at this point. Does anyone have any advice that might be useful. Thanks