Trish this sounds obvious but have you asked him why HE thinks he does these things?
He might not know of course. When i was 14 i was on the Pill and dating a 20 year old and when my mum asked "why are you DOING this?" i replied "Doing what?" and remember feeling so perplexed that she didn't get me wanting to be a grown up...obviously when i was 14 i didn't know what grown up meant!
I just wonder though if he thinks ahead at all, if he wonders what will happen next week or next month or next year if he continues to act like this? TBH depression and anxiety sound likely to me, but then how do you know? With this sort of thing, you just have to wait and see how they are at 20, and only THEN can you tell if they were the extreme end of normal or actually had some kind of problem happening.
Trish hun i really feel for you. It must be SO SO hard.
Lots of love
Bx