You mean the costs? Travel is expensive but I don't think there's much of an argument that it's gotten more expensive like housing. International flights used to be quite a luxury, now it's so easy that the popular destinations are getting swamped.

Most of the relaxation-oriented holiday industry is definitely designed for couples and families, but backpacking, adventures, and cultural immersion are, in my opinion, better alone so that you don't have the easy escape of sitting around with your partner. And if you want to relax nothing's stopping you from booking a few nights alone at a Japanese onsen or one of those treehouse style resorts in a Central American rainforest. I've spent many nights at onsens in between more outdoorsy climbing and skiing legs of trips in Japan.