well, one theory could be that he was never a real, nice person to begin with. that yes, you DID all those things FOR him, thinking you were helping him be a grown up, but it appears he may have just been along for the ride.
which is a reflection upon HIM, not you. i don't think, from what you've shared, that on a Monday he was the salt of the earth and on Tuesday he turned into this mean, spiteful, cruel man.