The fact that there's a word to describe female relations who haven't married says a lot about traditional expectations. Maiden aunts, spinsters.
I don't think there's a male equivalent.
Well, there's 'confirmed bachelor', although I agree that single women are more often seen as objects of pity than single men are.
I've just remembered I have two step-cousins as well, both of whom have never had a relationship. The female one has two DC via sperm donor, but she's never had a boyfriend and, for all I know, is a virgin. She's very shy and quiet, bookish, and rather serious. She's one of those people who you find yourself gabbling at just to fill the silences, because she doesn't talk much!
Her brother, who I don't know at all well, seems very into sports (all his FB posts are about how his team is doing
), is quite overweight and shy and I've never heard that he's had a gf/bf or anything else. She's 41 and he's 38.
I think there have always been plenty of people out there who haven't been coupled up. This thread shows that of most us know at least one person and in the past many people who were 'in service' never married. In the last century there were so many men killed in war that there weren't enough to go around so many women had no choice but to remain single.