Supergirl's origin story is basically Superman's origin story. Not being rude; that's just what's up. You know how Superman is from Krypton, the planet that was destroyed in that comic book that has his name on the cover? Great. That's kind of all you need to know. It's more or less that times two. Either way, Krypton exploded and now there's two survivors of all of Krypton. We thought it was just Superman, but no, there's actually also Supergirl - plus Krypto the Superdog, a bunch of criminals from the Phantom Zone and the entire Bottled City of Kandor. Basically, there are anywhere from one to around one million surviving Kryptonians.
It's kind of a sliding scale thing, but Supergirl (aka Linda Lee, aka Linda Danvers) is usually one of them. She was introduced via the comics in 1959 by Otto Binder, who invented Supergirl, Brainiac, Bizarro and pretty much everyone that anyone associates with Superman other than Jimmy Olsen, Lois Lane and Lex Luthor. That period of Superman comics are some of the most tripped out things I've ever read in my life, and Supergirl's stories are no different. That being said, there are some things you might not know about her. For one, her past relationships have been incredibly weird. Not run-of-the-mill, to-each-their-own weird. I mean weird. (This article in no way covers all of Supergirl's love interests, because we'd be here all night, but we couldn't help but spotlight some of the strangest ones.)
You remember how Superman is Supergirl's cousin and all? So does he, but he still tried to get with Supergirl in the 1960s more than once. There's a few issues where he makes out with an older version of her, and it is exactly as unsettling as it sounds. First, after Supergirl crashes to Earth and is revealed to be Superman's cousin, he sticks her in a run-down orphanage instead of adopting her. His reasoning is that he's using her as a "secret weapon" against his foes. Afterwards, he has Linda Lee dress as a vigilante named Mighty Maid and makes out with her for an entire story's worth of pages - Action Comics #260, in case you feel a need to go there. I don't have to point out the fact that she's 15, because Superman himself does.
The Superman/Supergirl romantic relationship hasn't really been revisited in several decades, apart from an incredibly messed up moment with a “mind-controlled” Supergirl in Jeph Loeb's unfortunate Superman/Batman series, but that's okay because it was quite bad enough the first time around. Pretty amazing that Linda Lee was related to exactly one surviving thing in the entire universe, yet still somehow found that thing and made out with it.
Jerro the Merboy
Her cousin was her first boyfriend, her second was Jerro the Merboy. He was also Supergirl's first non-relative kiss from what I can tell, so for that reason alone he's a huge improvement. He's a merboy and lives in Atlantis, aka the same city where Superman's Silver Age sometimes-girlfriend Lori Lemaris (an actual dang mermaid) also lives. That all immediately sounds just awful, but he's also from a race of telepathic fish people - so everyone knows what Supergirl's thinking about the whole time she's lusting after Jerro in Atlantis. He looks like he would show up playing ukulele on an ocean backdrop in Beach Blanket Bingo. Jerro kind of vanished out of continuity, mostly because he was a freaking telepathic merboy with perfect hair and thus everyone hated him as a character.
Tor-an is a villain who escaped the Phantom Zone just in time to make an appearance in Action Comics #307. He seduced and attempted to marry Linda Lee, because he apparently hated her so much he wanted her to live with being married to a bastard for the rest of her life. First off, the poor girl has probably hit her "complete bastard of a boyfriend" quota by now. Secondly, that really is the most effective super-villain plot of all time. Marrying her and then treating her like garbage for the rest of her life is probably the worst thing you could do to a 15 year old girl, so nicely played. There was a character based on him in the Supergirl TV series, but nothing he or really any villain has done since tops marrying someone just to ruin their life.
After Fish-Guy, murderous villain with the longest long game of all time and her creepy cousin, there was a time when Supergirl actually had a girlfriend named Volar, who appeared in Action Comics #384. Volar crossdressed to avoid persecution as a woman on her totally bizarre planet where the female citizens are treated somehow unequally to the male citizens. Part of what is so hilarious about this story is how deeply sexist comics of this time are, and yet Supergirl is ABSOLUTELY STUNNED that there is a planet where women are deemed inferior. Folks, we are breaking the fourth wall. It is meta as hell.
Ultimately, Volar whips her mask off and the narrator of the story says, "Well, she's a girl, though! Everyone know that two girls can't kiss, so, that's a wrap!" Supergirl doesn't seem that freaked out by the gender reveal, not to mention Volar knew her own gender even if Kara didn't - and she still wrote love letters to her. Maybe it's time for Volar to get resurrected so these two can have a happier ending?
Comet the Super Horse
Full disclosure, this is about to get intense. Are you ready? Okay, great. Supergirl straight up made out with a horse. In fact, a Super Horse. Because sometimes the Super Horse is man-shaped, and he doesn't tell Supergirl that he's actually her horse, because he's the worst “nice guy” stereotype ever, but also a horse! This is weird enough as it is, but then we have to deal with reading Comet's thought bubbles while he's in Super-Horse form, staring at Linda Lee like a total creep.
The best thing about the Comet debacle is that he was retconned out of existence, and then was actually brought him back as a lesbian comedian who sometimes turns into a half-horse guy that... Supergirl also makes out with. It's not less weird the second time around, that's for sure. Also, speaking of critical mass moments in pop culture, retconned Comet the Super-Horse, with their pink and silver manga robot horse costume, is for sure nerd culture of the late 90s hitting critical mass. Unfortunately, it's also one of the creepiest stories ever.
The Supergirl movie isn't even a camp classic, but it should be because it is peak 1985. It features Faye Dunaway as an evil witch character, Mia Farrow as a mom and a cameo by Peter O'Toole. That is the supporting cast of literally every movie made in the 80s. This film introduced another boyfriend for Linda Lee: a groundskeeper at the prep school named Ethan. Ethan is amazing, because he walks around speaking in really bad poetry and carrying flowers and declaring his love for Linda Lee even though he doesn't know anything about her. Somehow it works. She spends most of the movie saving his life, then they make out. Nice.
Supergirl stayed dead for a shocking three whole years before being retconned back into continuity. When they brought her back, it was an absolute mess. She was reintroduced as a shapeshifting alien that was later revealed to be a clone that Lex Luthor made, because God knows Lex Luthor has to be responsible for everything that ever happens in a Superman comic. In an incredibly whack move, he began dating Supergirl who, once again, he literally made in a lab. In the late 80s and early 90s, there was a younger Lex Luthor with a full head of bright red mullet. He said he was Luthor's son, but it turned out that he was just a younger clone of Luthor, blah blah blah.
Before any of that is revealed though, Lex and Supergirl were together for a few years in the comic, and in case you're wondering, it was absolutely a thousand percent exactly as wrong as it sounds. Mostly, it involved Supergirl walking around like "La la la, I think Lex is just such a sweet guy despite all existing evidence to the contrary, la la la." It was so problematic that listing how problematic it was would be its own article, so I'll keep it brief: killing Supergirl off and then bringing her back with no identity running after Lex Luthor like a puppy issue after issue was painful to watch.