I suspect part of the reason why you don’t see that many truly married characters in superhero comics (or any adventure comics), let alone characters in actual long term relationships without convoluted nonsense is that it seems either boring or maybe some are just too private to depict married relationships (the latter seems likely). Another one, if the Flash comics are any indication, is that the girlfriend in question would be a nag. Or in Spider-Man’s case, she’d emasculate him in some way by being better than him in something else.
She could be wealthier (Mary Jane) or possibly much better at sports/physical activity than he’ll ever be (Big Barda, Wonder Woman and Supergirl to some extent). Though keep in mind that some writers seem comfortable enough to have the super-strong, brawny likes of Big Barda and Supergirl date/marry highly intellectual/academic men. Whilst others seem to have trouble considering the odd possibility that Stephanie Brown might be kilometres better than Tim at sports.
(Though one wonders if Supergirl, Wonder Woman, Jean Grey and Big Barda get away with this by the virtue of being highly exceptional, supernatural women that does excuse them from certain criticisms that plague poor old Mary Jane and Iris West.)
If that’s case, I guess the more normal a woman is whenever she starts emasculating her male counterpart the more hated she gets even if it’s not always nor consistently the case (especially for Wonder Woman and Supergirl). But it still makes sense that there’ll be attempts to knock them down. Look no further than what’s been done to Big Barda. Ad infinitum.
There are a number of Spider-Man readers who can’t stand Mary Jane, finding her emasculating on the belief that she outearns Peter Parker and preferring him to be with Gwen (who in reality wasn’t any better early on). There are a lot of fans who can’t stand Iris West, black or white. There are some who consider her to be a mean little shrew.
Even before the CW programme aired. Whilst Steph’s an already polarising character, should she turn out to be better than Tim in sports and nag at him whenever he refues to help her in caring for her family and doing household duties fans will surely hate her for being a ball-breaker. And partly why domesticity rarely happens in superhero comics. Nobody wants a nagging wife/girlfriend.
Nobody wants a girlfriend/wife who’s stronger or better than him in some regards (look no further than what Mary Jane gets). Alternately speaking, not too many superheroes have children. Let alone allow them to grow up and have children or at least learn to look after younger relatives in general for extended periods of time, even if they may not always raise them right (Jojo’s Bizarre Adventures or X-Men comics to some extent).
This might partly account for why at least in the magazines writers never allow Spider-Man to grow up. Never mind that early on in the comics he was actually mature for his age (having to look after his family and a job whilst studying). Similarly, we never get to see Steph look after younger relatives for long even though other characters are allowed to do this (Donald Duck, Jotaro Kujo and his grandfather Joseph). But that would necessitate situations where she’d nag at Tim for not helping her around.
The only few characters allowed to actually raise children or look after younger relatives in any way, even if it’s flawed are generally rather a few. These include Invisible Woman and Mr Fantastic, Superman (at times), Jean Grey and Scott Summers, Roy Harper, Wally West and the Invisibles to whatever extent. When I mean by that, most superheroes rarely look after biological relatives.
Just a few of them actually do it often. But that would mean necessitating the character to mature for good. Jotaro Kujo went from a delinquent to a loyal mentor to his younger relatives even if he still screws up. Donald Duck’s sometimes responsible for his nephews. Even Peter Parker has to be responsible for Aunt May. There won’t be any illusion of change in here.
Especially when they have serious familial obligations to do, they can’t go back to being children again. That’s a strong contrast to the usual superhero get-up where if a superhero turns out to have a younger relative they let other people babysit them. This is what Supergirl usually gets and we rarely see her hang out with fellow Kryptonians.
If superheroes are supposed to be a childish power fantasy, having them get to raise younger biological relatives ruins this. But that would mean characters would have to become adults. The younger relative might be a nephew/niece or even uncle (again in Jojo’s Bizarre Adventures, the first lad Jotaro mentors is his much younger uncle) or an actual son/daughter (X-Men has this in spades).
You could age up that child but once that happens, characters like Jotaro and Scott can’t go back to being children as they’ve got a younger relative to raise and care for. And why the illusion of change thrives on minimising or eliminating the possibility of familial obligations and domesticity for most superheroes.