He wants to do Anal but I hate it!! Help!

He wants to do it often and don't get me wrong I've tried it and I literally hate hate it everything about it and when we did try it I felt like crapping the whole time and it's a big turn off ...what do i do!!?? I feel bad for telling him no but seems like he really likes it How do i get over the fact that I hate it and won't do it...Help!!