I share your view on relationships and wondered about this too. Basically my SO and I have made it our goals each to provide the other with freedom as much as we can. This is a maintenance things as well as evolution. Unlike my SO I don't have a dream job and don't like working much (I'm not lazy, I'm a good worker but I get no sense of purpose or self out of it like most people seem to do) which is why I want to try our very many different things over the next few years and he, being in his life time secure job, wants to offer me as much freedom as he can for me to pursue these ideas. Likewise I work on being interested in his ideas and goals. He's very much into traveling and having hobby goals like getting good. VR gear, new technologies, but also motorcycling etc.

However in the end none of these are as time consuming and constantly pressing as kids are. And that's exactly why we're cf. We don't want such a big common project like kids because we'd lose too much of everything else. It's not even just kids. We'd like to buy or build one day but we'd never take on eg renovating an old farmhouse over the course of ten years.

I think empty next syndrome is basically the same sentiment that us cf might have 20+ years earlier of "that's it? What now?" The answer is always the same: yep, that's it, just carry on line yesterday.

Evolution is a great thing in a relationship but it's not necessary. It can be simply good as it is for a very long time.