First order of business, you need to think hard about whether it might be best to declare this a hard limit and take it off the table completely. If so, you’ll need to have a talk with him about that. If you’re not prepared to do that, then come back and we’ll see what my Followers can come up with to help.
Jesus, what is it with anal anyway? I mean, it can be nice but people treat it like the holy grail!
Some people like getting their asses played with. Some love it. Some can even come that way! But…
Not everybody enjoys getting their ass played with!
I’m not talking even about prudery or “inhibition” or embarrassment or “one way only.” I’m talking plain old every day doesn’t work. As with the anon some people just feel like they’re taking a dump. Or need to. For others it just hurts. For others it’s just disgusting.
I talk about stereotypes a lot. One stereotype about gay men is they all fuck each other’s asses. So if “anyone” ought to know about anal sex it ought to be gay men, right? Little clue though: about half of all gay men don’t like anal either. And don’t do it. And at least according to gay friends I’ve talked to totally, unremarkably fine in the gay community. So yet another stereotype about gay men shot down. But I digress…
As for the anon, the answer likes in the question. Put the plugs in your ass and report if you enjoyed it! And answer honestly, clearly, and sincerely that it’s uncomfortable, unenjoyable, and not erotic either in terms of sensation, submission, or masochism; that you’re scared of losing him and of ass play and that while you don’t want to lose him you also don’t want anal.
His answer may help the anon make their decision! If they’re any kind of a decent top, partner, lover, or human being they’ll listen.
And look, it’s actually pretty likely the Dom will totally get it and say let’s do something else then. Because contrary to popular opinion most actual Doms like and care for their lovers.
But the bottom line (yeah, sort of a pun) is that any kind of sex, and any kind of relationship, has to be satisfying to all partners and not just the top. One can define “satisfying” as one wishes, which is why some people will do things that genuinely disgust them because it pleases them to please their partner… but that doesn’t sound like the anon’s situation. (If it was they’d have phrased their ask differently.)