I think once it's gotten beyond the year mark, then it's..... worrying for the future.
Unless of course you both have the sex drive of a sloth, which does happen of course. And those marriages tend to be fine, as its fundamentally two fairly asexual people and they find it easy to separate sexual love from romantic love.
But most of us are not in fact asexual. And really like that romantic love leads to sexual love. And find sexual love definitely enhances the romantic love. Stops it ebbing away.
So if one of you has become asexual and effectively ended the sexual love, then I think for a person who needs the mix, it's a situation they will struggle in.
And I have read a lot of threads on here where women are shocked (SHOCKED!) when their husband blurts "out of the blue" that he doesn't know if he's in love anymore. And about 3 pages in there is a brief mention that they have had sex about 3 times in the past 18 months or even less, but everyone glosses over that to support OP, who is absolutely floored that the lack of sexual love in her marriage has eroded the romantic love.
Look at the current thread about the guy who is having too much secret texting with the celebrity. All along it was: "It's just hard because other than this, I have no issues in my marriage. We don't really fight, our routine with the kids is like clockwork" Total bafflement that they may be slowly grooming each other for an affair. Why? When everything at home is fine??!
Today the little drip feed that OP and her DH haven't had sex in over a year.
People get very very defensive about this subject, but there is no doubt being in a sexless marriage can absolutely corrode a marriage for some.