And some genders too for flavour I suppose.
Bastion is asexual and has no gender or sex. (They weren't assigned one, so by some definitions they might count as cis.) I'm not sure if they're completely aromantic or somewhere in the greyromantic zone; I've enjoyed shipping them sometimes but not drawn any definite conclusions.
Having romantic feelings would be rare and surprising for them; if those romantic feelings were for a human, as opposed to another omnic or a fantasy creature or an alien, they'd also be conflicted and disbelieving about it. They aren't a big fan of humans as a group and putting their trust in an individual human is difficult.
Wilson is ace, biromantic, and grey-aro. He's from a time period when most of these things didn't have their own labels; what he knows is that he's theoretically capable of falling in love with both men and women but doesn't actually experience those feelings often and considers the act of sex highly overrated.
I headcanon that he dated another male student when he was in college but they broke up by the time he left academia.
(Not a canon character, just some guy.)
At PH he considers himself to still be dating Maxwell, from his last game, even though it's been months without any sign of him. (The player does intend to bring Maxwell over eventually but hasn't yet beyond a few TDM threads.) Which is like... narrowly my favourite same-canon ship for him, but I ship him with a lot of people.
However I'm very picky about Maxwil. It has to have the right hatemance dynamic. Not too toxic or too fluffy.
Which we achieved in the last game! Then the game exploded.
Also writing romance is hard.
Which may have something to do with why I play a bunch of aro-spec aces.
The Ancient Fuelweaver technically counts as a bisexual cis man but he comes from a nonhuman society with four main genders (plus various nonquaternary options), so the valences are off. He's bi insofar as he doesn't have a gender preference strong enough to insist on it when dating across species lines, and most of his potential dates are human.
And even the nonhumans are often pretty human-shaped.
He's not really looking for love, but those are the parameters.
I'm not sure if there was anything non-normative about his sexuality by the standards of the ancient Thulian civilization. I'm not really sure what the norms were in the first place.
Moiré is also grey-bi-romantic and ace. And from 2017, so they know those words. They had a mild crush on a dragon woman changeling in their original campaign but didn't do anything besides follow her around like a duckling. They've been attracted to multiple genders, but not enough times to have a clear idea of whether they have a preference or not.
I haven't committed to anything in particular for the Purple Impostor, but they're not very flirtatious and try to keep people at arm's length.
Bi, aroace, or bi ace is generally a safe default assumption for characters I play, though; if I play someone as straight that's an authorial choice, not a default. (Well, or their canon did in fact establish that they're into the opposite binary gender and only the opposite binary gender, but that's honestly fairly rare.)
Wormwood is really hard to fit into the standard model of sexuality. He has a completely different reproductive system from a human, which doesn't require a partner, but he does enjoy the process of asexual reproduction. He's not physically attracted to meat-people (or robots or whatnot) and has never met another plant person.
Calling him asexual under those circumstances seems misleading.
He could fall in romantic love without being physically attracted, and doesn't have a strong gender preference in that regard. Having very little experience with either, he doesn't have a clear idea of how romance is different from friendship.
Aradia and Cirava are bi, which is normative for Alternia.
Aradia had a quadrant filled before she died, but was cagey about which one it was. Personally I think she and Sollux were moirails.
Cirava didn't have any quadrantmates left after The Incident, if they had them before.