Help Please!

My boyfriend and I have been dating for a while and we've done a bunch of things (sexually) but recently he asked if he could eat my ass. I don't know how to respond because i think it's weird. He keeps insisting on it because he wants to know what it's like but I keep holding him off on it because it just seems a little off to me. Thoughts on what to do? or experiences on what it's like and how it felt to you if you guys went through it? I just want to know. Thank you!