I mean this in the best possible way, OP, but how did you envision the future for your son and any girlfriend? Would you also be running after them to take care of clothing/work/possible babies/food/rent.... Did your DH agree on that vision?
I have difficulty understanding how this has gone on for so long. They don't need you to foresee "living life" anymore do they?
At 20, I didn't have a driver's license because I couldn't afford lessons. My mum couldn't either, she had other mouths to feed after dear old dad skipped town.
I took the train, bus and metro. Got lost quite a few times, too
But I guarantee you, I wouldn't have wanted my mum trodding along to make sure I got where I needed to be.
I have a son, who's nearly 9. He has chores tailored to his age, that will make it easier for him later on, but he still has responsibilities! Help with dishes, feed the animals, helping his parents to keep the house in order, cleaning up after himself.
All those things you tried instilling in your son, he hasn't forgotten them, you know? Time for refreshing some basic skills for your 20 year old son, and for you to re evaluate how you're parenting.
Good luck!