One of the nastier features of the relatively recent civil wars in parts of Africa has been the way that children demonstrate a far greater propensity to cruelty than adults. This reflects the fact that they don't really understand the way that their actions impact on the lives of others - and this is reflected in the fact that most jurisdictions have an age of criminal responsibility below which a child can't be convicted by the courts of a crime. So don't be too surprised that he's no idea of the impact on you - he's just not used to thinking like that.

Another possible motivation - and this isn't exclusive of anything else I've said - is that he's learning about controlling his own life. He's reached an age where instinctively grabbing control of what's in his life and trying out what he can and can't do. And of course being a teenager means rebelling against what your parents want: you are in favour with his parents so it may be that at some level he's just kicking against that. IF that is the case, it is possible that he will come to realise that he's made a big mistake and want you back - so you'd do well to leave the door open for him to slide back into your life without having to crawl / make a big apology. Maybe think in terms of suggesting doing something together at Christmas (when Christmas gets here - don't suggest it now) - enough weeks away that the dust will have settled. Just don't bet on bringing it all back.

But what this is, is a wake up call for you to sort out those elements of your life that are a mess. God has given you gifts to use. One of those seems to be an ability to mentor boys, and there are no doubt others. It would be great for you to be able in a few years time for you to look back and realise that this hurt was the thing that resulted in your becoming 'a really useful engine' - to quote the Thomas the Tank engine books...