I don't know, my husband and I still have a lot to talk about, still find each other attractive, and still have a good sex life. But, he's also always been my best friend, and we work at keeping the romance/sex part fresh. All long-term relationships involve some effort, but I wouldn't say that it's actually difficult to stay attracted to someone you actually liked all of right from the beginning.

Here's something I wrote recently about keeping things interesting.

https://medium.com/sensual-enchantment/the-romance-of-the-shower-orange-30616caadaca