<human>: Can you summarize the given text in a few sentences?

I've been with my boyfriend for about four years, and when things started out he was extremely...vanilla. Being no stranger to kink, I attempted to introduce him into bdsm and some more interesting aspects of sex. 
Fast forward to a few months ago, and he wants me to start putting a finger in his ass. I say "great! You'll love it!" And he does. 
Soon, one finger isn't enough so he wants two. Then he wants four. Then he wants a fist. Then he wants a soda can and a strap on at the same time. He wants it to bleed. He wants it to stretch, he wants more and more. 
I can't handle the blood. I can't handle the extremes that he is looking for, but I feel like is getting to the point where he doesn't want to have sex unless I'm literally tearing his ass a new one. 
I don't know, maybe this is the wrong sub for this, but I'm at a loss. When I met him he was so put off by the thought of something in his ass he would stop any and all sex if I even suggested it.
<bot>: my boyfriend only wants to have sex if I have my fist in his butt and I don't want to do it anymore :(