God, I want to stop breast-feeding.

I cannot stop breast-feeding.
She’s almost 19 months old, for fuck’s sake. When people hear I’m still breast-feeding, their reaction has gone from “Good for you!” to “. . . Really? Still?”
I have not really developed another way to get her to sleep, though. I know that’s bad. I know that, starting at about four months old, I was supposed to start putting her down in her crib (hah!) when she just looked drowsy so that she would learn to fall asleep on her own. I did not. Bad Mommy.
She bites me. She does it for fun. She clamps her teeth down on my breast and then pulls my nipple through them. When I cry out in pain, she laughs. I can’t take it any more.
But she loves breast-feeding! She hums! She looks deep into my eyes. She says “Mama” in this sweet, grateful little voice. She just looks so damn satisfied doing it. How can I take it away from her?
What am I, supposed to do this forever? SHE’S 19 MONTHS OLD!
But she’s doing so well! She’s so strong, and so smart, and so happy! What if this is all due to the fact that I still breastfeed her and let her sleep in my bed? What if, when I stop, she just shuts down?
That’s ridiculous. Also, this is ruining my life. I can’t be separated from her for that long, because she might need to latch on. We can’t go out at night. I can’t get up early to work out; who knows when she’ll need a breast-feeding?
She bites me. And she pinches me. And she doesn’t eat much of anything else because she knows she’s just going to get breast milk so why should she? I must stop doing this.
I can’t stop doing this.
I don’t know what to do.