How do I help my disabled Step-son understand it takes time to fall in love?

I have a severly disabled 20 year old step son who desperately wants to feel the closeness of a woman. He was hit by a car when he was 10 years old and now suffers from traumatic brain injury and is semiquadroplegic. He frequently gets upset because he has not found a girlfriend yet and I have tried to explain to him that love happens more when you don't try. He frequently comes home from school saying he has a girlfriend but most times these girls concider themselves just friends and he doesn't understand why they don't want more. I am worried that this is eventually going hurt him so much that he won't want to continue living. Actually have had this conversation with him a few times. I try to tell him just to enjoy life and if a woman comes along then great but if not then live to love what he has.