Less sleep, definitely, and maybe less time working out—relationships take up lots of time, even if you're not with someone who's especially needy. Very easy to

Less sleep, definitely, and maybe less time working out—relationships take up lots of time, even if you're not with someone who's especially needy. Very easy to let one's workout routine slip to avoid cutting in to other solo activities too badly. Even worse if you add kids to the mix. Less time hittin' the weights means lower T. (obviously plenty of couples work out together and still get some exercise in that way, but even then either or both of time and intensity could drop compared with when single)