You can not live some one else's life for him, (or her).
It is futile to invest more effort into his life than he does for himself.
I have a doctor whose philosophy is that she'll work as a partner for her patient's health, exactly as hard as the patient is willing to work.
Back when I was in college, one of my buddies had a diabetic friend. My buddy believed in "tough love." When his friend said "please get me a drink from the 'fridge," buddy said, "I shouldn't have to wait on you in your apartment! I'm your guest!"
The diabetic was blind from his disease...earlier than he had to be. He had threatened his girlfriend that if she broke up with him, he wouldn't take his meds, (she'd been conned by him into giving him the injections), and his condition would be her fault. He did show up at her apt after several days, weak and sick. She closed the door on him and called an ambulance.
You know what? He deserves to have a great life and love, as much as you...and if you know you can never feel about him that kind of love, and if you have the stones to end it, more power to you. I figure if YOU KNOW, you'll never love him again, you're not doing him any favor by sticking around and pretending you will.