Hugs for your hurting mommy heart.
This is a VERY tough situation to be in.
I know you do miss him, and you probably are missing the kid he once was. You are probably also grieving the man he "should" be. That is hard. "Our" kids don't necessarily reach milestones at the same time as other kids, and that doesn't stop when they turn 18. My daughter turned 18 and moved out of the house and in with her b/f that day. Is that what I wanted for her? No, not at all. She had such potential, and I wanted to see her go to college. But it is her life, and there is nothing I can do about it. Detaching was hard.
She just turned 20 at the end of March. She is still with the same guy. They are doing OK. Not great, but they are doing OK. They both work. They pay their bills. But, they live with the b/f father in a shady part of town. And they still get high.
I'm not thrilled about it, but they are not coming here asking for handouts either. She seems genuinely happy, so I am happy for her.
Sorry, did not mean to hijack your thread. Just wanted to let you know that you are not alone.
(((hugs)))