My boyfriend (28M) only wants anal from me (25F) advice?

So we've been together two years. My boyfriend (28M) recently started having this weird obsession with anal. I've (25F) tried it over and over with him and i just absolutely hate it. He is also very thick.. it's just something i don't think i will ever like no matter how hard i try. This maybe be TMI but I also have issues with being constipated sometimes and just rather not have anything up my butt. It feels like he never wants to have vaginal sex. I'm kind of at a loss for words and I'm just getting annoyed with it. Advice?

I should also add that we’ve always had an AMAZING sex life, we’re open to each others kinks, etc. And he’s told me I’ve been hands down the best sex he’s ever hard. I just feel like now I’m failing at that.