Isn't it funny how God instills in us (most of us) the longing desire for children and then once we have them we long to be rid of them? So funny. Bobono, I'm going to give you the solution to your problem, but first I'm going to make some unfounded assumptions. First of all, I'm going to assume you make his life far too easy. If you are currently doing any of his laundry, clean up, or feeding him in any way you must cease and desist immediately.
You see, sons cleave to their mothers because mothers never stop mothering and sons never stop wanting to be taken care of like little baby boys (even when they're 36 and married with kids of their own). Unlike daughters, who run like hell from their mothers for fear of turning into the one woman that drives them over the canyon wall. Bottom line, stop treating him like a child and more like a tenant. I hope he is paying rent, if he's not, he should be.
Now, about him living in your basement and not going out much. Here's what you do to motivate him to get out in the world: start having sex in places he might walk in on you, like the kitchen, the living room, his bed...you get the idea. That is a sure way to creep him out if it doesn't blind him. If that doesn't work then let him catch you measuring a space in the basement and when he asks what you're measuring tell him, "I'm having a sex swing put in. You don't mind do you?"
If he won't go to college (and let's give him some applause for having a full-time job) then it's time to start a grown-up life and grown-ups do not live in their parent's basement. If he wants to delay joining the adult population then he needs to get his butt in college. But if college really isn't for him (and it's not for everyone) then it's time to tough love him out of the basement. Sit down with him and tell him you love him, but he needs to have his own space. Then put together a timeline for his departure and your expectations for his exit plan. Maybe suggest a roommate.
Now, the larger problem of friendships and a rich, fulfilling life. Sadly, and luckily, we cannot live our children's lives for them. Children must make their own way in this world while we stand back and pray they don't fall flat on their face. Even my four year old must navigate the snarky playground on her own, and though I can hardly breathe watching her walk up to a group of older girls and asking, "Will you play with me?", I have to stay on the sidelines, letting her make new friends or learn that not everyone says "yes."
Parents have so many dreams for their children, but sometimes our dreams for them become expectations, meanwhile we forget that our dreams may not be theirs. Remember, 19 is still so very young and he has a long road ahead of him. I didn't figure out what I really wanted in life until my thirties! If you haven't had a discussion with him about what his dreams and expectations are from life then now is the time. Not necessarily, "what do you want to be when you grow up?", but what do you want your life to be? What fulfills you? What gives you joy? He may not have answers now, but he never will if he does not start with the questions.
When he begins an independent life I suspect he will develop friendships, it might not be party all the time, but it will be his own life. And if along the way he makes only a few good friends then he has all he needs. One good friend is worth 100 casual friends.
But I do understand your longing to see your son have the full life you envision. Sometimes with Sam I can feel myself longing for her to be the sweetest, funniest, kindest, smartest, most everything girl, but she'll never be all of these things all of the time. And some of them she will never be, but she will be who God planned and who I helped shape. And that will be enough.
Keep loving your son to the fullest, but love him with strength and set him on his own path. He will find his way, most of us do eventually. Trust that he will find the friendship, love, and laughter that he is comfortable with and that he needs.
One final thought, consider the possibility he is suffering from depression (again I'm making assumptions about his behaviour) and the benefits of therapy and/or medication (you know I'm now a fan).
Bobono- loving your children is the greatest gift you have to give them and I have no doubt you have given them double.
Now, help him, help himself.