When is it time to give up?

So my problem is that I love my boyfriend. We met when I was fifteen, and he told me pretty quickly that he had crohns disease and I told him I could handle it. We started out hot and heavy, morning, noon and night type of thing, but when I was 17 his health declined a little. His sex drive was low, we stopped going out and started hanging out at home.

I started putting on weight and had gotten my GED, Nick doesn't have a job because of his condition, so we just stayed home. Our life became a tiny bubble, not moving forward just floating.

Nick used to be charming and romantic, but now I feel alone in a house we share together. He's lazy too, the apartment is a mess, the kitchen looks like it should be condemned, and there is laundry every where. Any time I make any sort of progress the crap just piles up again. Some time we go months without having sex, I look in the mirror and some times I just hate myself.

And now our bubble has popped, we have to be out of our apartment in 8 weeks, we have no money, Nick borrowed $400 dollars from me a few months ago and haven't seen it since. Every time I ask about it he just changes the subject.
I'm trying to move forward, going to school, weight watchers and getting my drivers licence, but Nick just seems like his head is buried in the sand, gripping on to our bubble for dear life.

I want to marry Nick, and have a family. I love him. He has always treated me like a princess, Nick is safe, Nick is secure. I feel like if I were to leave him no one else would want me. I don't have many friends and no one to talk to. I've put 3 1/2 years of my life with this person, But he 26 years old for crying out loud!

I threaten to leave and nothing changes, so I guess what I want to know is, What can I say to make him realize that he is going to lose me?

Nothing you can say will work because he probably just does not give a shit does he? So leave the sad idiot and have a life worth living. Aren't you worth that?