This is my smut entry. I'll try to keep it fairly clean in terms of words but we'll be talking about some adult stuff, so if you want to skip this, now would be a good time.
I was thinking about sex and superheroes this morning on the drive in. Most comics just ignore it and that's a perfectly fine genre convention to keep.
If you want to go all hardcore (so to speak), go off and read Larry Niven's famous essay, Man of Steel, Woman of Kleenex. (The Wikipedia article is here, and a probably illegal copy of the text is here. No guarantees that either link will be good even a second after I post this.) I'm proposing something a little gentler.
For starters, let's ignore all the trained and gimmick-laden humans. They have no physical problems. (Maybe mental ones, but that's outside my purview right now.) We can probably not worry about lots of mutants: if your mutation is that you have wings or horns but everything else is standard equipment, you don't have a problem except maybe socially.
That leaves us the folks with powers that make things difficult or who aren't actually human: your super-strong or invulnerable types, your rapid regenerators, your superfast speedsters, or your aliens. It's not clear if Metamorpho even has genitalia any more, though he can probably produce something suitable.
The super-strong or the invulnerable might be in danger of hurting their partners or of, er, not being accessible. If regenerators happen to be capable of regenerating and there's a noticeable hymen, that might be a problem. Speedsters probably have a problem syncing up with their partners.
The obvious solution, and one that might feed nicely into any campaign that features any kind of super/non-super stratification, is that supers of that sexually-isolating kind only date other supers.
There's something terribly lonely about the woman with the permanent force field who can only date the person who nullifies force fields, whether a hero or not. The Obelisk might pine for Nancy Normal, but can only be intimate with Suzy Strength. The Zipper might remember her old boyfriend fondly but the foreplay takes so damned long (hours by her standards, even though he's known as Quick-Draw locally). And Quirk the being from Planet Z doesn't even find humans attractive, but dolphins work.
There's a subclass of supers who can only have relations with other supers, because they're afraid of hurting a normal partner. (I suppose there's a subsubsubclass of those that doesn't care about hurting a normal partner, but I prefer not to think about that.) So what kind of things are you going to see developing because of that?
MetaDate is the online dating service for metahumans. The customers (with exceptions, obviously) have a higher tolerance for unusual appearances. Gender categories include male, female, trans, neuter, and fluid. The profile form includes relevant powers, but they never ask which side of the law you're on.
The Underground is a dating club for metahumans. It can be classified as either a place for a date or a pickup bar, depending on what section you're in. The Underground is, well, underground: under an embassy of a country without an extradition treaty. In fact, it has an agreement with the embassy: activities on its soil are not considered to be bound by the laws of the host country, and while they might be technically illegal in the embassy's country, there is no access between the Underground and the embassy. The embassy's staff practices "don't ask, don't tell." The Underground is not a place for actual assignations; the staff is quite strong and there are other staff members who handle some of the more outre abilities. (There is a member of staff normally immune to suggestion or mind control, for instance.)
Dimension X has nothing so abstruse legally...it's just a place for aliens. It started small, and is gradually growing to fill the warehouse block where it exists. There are a number of small rooms, each of which attempts to mimic "home" for some alien species. Most of the rooms can handle a number of environments, but the number isn't infinite, and there are some things it can't handle at all. They used to have a problem with theft (supervillains kept stealing their gravity repulsor technology or their red sun filters) but a few retired heroes work there now, and that has lowered the incidence considerably. It is expensive, though the local agency that deals with and controls aliens (the Bureau of Extra Foreign Affairs) supports it.
Uplifted animals have different problems...but that's for a different post.