At 37, I am likely looking at a future of turning 40 without being married. It is unknown where things will be in terms of romantic relationships at that point, but it is highly unlikely I'll have a settled, stable family situation on my 40th birthday.
I would be more likely to be a serial monogamist in my 40s than a plate spinner. Neither serial monogamy (changing out committed girlfriends every 1-5 years) nor plate spinning are phenomenal ways to spend one's 40s, but there are worse ways to spend one's 40s.