Chickory, I just want to offer you hugs. I know you might feel cornered by your circumstances, but you have gotten wonderful advice here. I really like Learn2Live's insight about our children--it's true.
I always try to live by Kahlil Gibran's words "On Children":
Your children are not your children.
They are the sons and daughters of Life's longing for itself.
They come through you but not from you,
And though they are with you yet they belong not to you.
You may give them your love but not your thoughts,
For they have their own thoughts.
You may house their bodies but not their souls,
For their souls dwell in the house of tomorrow,
which you cannot visit, not even in your dreams.
You may strive to be like them,
but seek not to make them like you.
For life goes not backward nor tarries with yesterday.
My brother-in-law sounds a little like your son... seems to be unmotivated, just a little unable to form the connections that will get him out into the world in a positive way, but otherwise is a good guy, funny, nice.
But my MIL constantly did for him--paid for everything, paid his car loan, bought his food (and when he went to the supermarket he bought without one bit of consideration that this was his mother's Social Security money he was spending so frivolously).
Now she's gone, and he's going through a tough adjustment--NOW he's looking at prices of things, and figuring out how to pay his bills. He's pretty shell shocked, but he's doing it.
Please try to see that doing for our children stops being a blessing when it stunts their growth.
Hope you're feeling less hopeless today, Chickory!