How often y’all having sex?

I’ve been with my fiancé for three years- getting married next month. We were hot and heavy at the start of our relationship, having sex all the time. About a year in our frequency dropped pretty substantially and it’s only getting worse. I have to ask for it for about four days straight before I get a “yes” and we’re doing it about once a month. We’re young (late 20s early 30s) no kids, and live together. We talk about it, he says we’re having enough sex for him and when he wants it. He says he has the right to say no. Everything else is smooth sailing — except sex. He never offers suggestions to fix it. Not that it matters, but to be frank, both of us are in really great physical shape and are attractive, no recent changes at all.

Yes, I know he’s watching porn and doing himself in between, so it’s not like he’s not interested.

Any suggestions?! Is this normal? How often (honestly) is your norm?