King was irrevocably, irreversibly, madly in love. There was no other way to say it. And really, who could blame him? She came into his life like a surprise deathclaw attack; that is to say he didn't see her coming, and by the time he did? His chest had already been clawed open, and his heart put into her capable calloused hands.
He hadn't thought much of her at first, beyond thinking her as pretty, in a rugged sort of way. She had turned up out of the blue, covered in dust from her time in the Mojave, and followed by a First Recon and an eyebot. She gave no introduction, and just asked after any work he may have for her. She was nosy, inserting herself into things she had no business being in, he honestly hadn't thought she would last more than a day. But then she started making real lasting changes, actually helping the people in Freeside. There were less chems on the streets, and everyone had more ready access to food and water, that most of the things she did ended benefitting him in some way? Well, he certainly wasn't going to complain, and he was more than happy to send a few gifts her way in return. She had even managed to stop the fighting between his Kings and the NCR, he still wasn't quite sure how she managed that one. Oh, he knows how she convinced him, there was no way he could say no to her when she leveled him with those big brown eyes and said please. But the NCR? He couldn't see them falling for that one.
But the real kicker? The final nail in his coffin? The thing that made him realize just how far he was gone for her? She had saved his Rexy, and had been adamant on doing so once she'd heard he was sick. She'd been gone for barely a day after she found out his beloved Rex was sick, and had come in practically bouncing with excitement over her found solution. Maybe he should've realized at that moment, just how much he cared for her, because he agreed to send Rex with her, not even really expecting them to come back. But they had, just a few days later. She with a beaming smile that lit up her whole face, and Rex with a pep back in his step. He… had never seen her smile before, not like that at least, so fully and so happy. And he decided then and there, he wanted to see that smile as often as he could. That he would do just about anything to do so. So he sent gifts, had every member of the Kings carrying something for when they saw her. Simple things from filling foods, all the way to hard to find super stem packs. He let her take Rex with her out to the Mojave, it gave him some peace of mind knowing she had Rex (a piece of him) with her. Sure, the Recon Sniper probably wouldn't let anything come near her, but Rex was as loyal as they came, and he wouldn't let even a radroach within a 10 ft radius. That she came to visit often so he could see Rex was just a nice added bonus. (and when she eventually came to him with her pleading big brown eyes and asked him to please stop fighting the NCR. it was all he could do really to even put up a token of a fight.)
As blinded by his love for her as he was, he could also recognize when there was less than a chance in hell with someone. He would always give her gifts, and he would always do everything he could to make her smile. But he'd seen her with the First Recon sniper. Her smiles came easily and freely for him, no gifts necessary, and with them the icy man would melt, even just a bit. They fought and bled together out in the Mojave, and their bond was all the stronger for it. He'd known a few retired military men in his day, had a few currently in the kings, he knew they didn't relax. And that the sniper could easily do so in her presence? And that she, who had been betrayed, shot, and left for dead in a shallow grave, could do the same? Was nothing short of astounding shared love. The two circled each other, stuck forever in the other's orbit. So King would flirt, and he would bestow gifts, and he would even serenade, forever pushing his luck that the Deadly sniper will one day lose his patience with him. (he knows there are days where he's come close, where his only saving grace was her laughing him off, and telling him that she was thankful for his friendship.) King would hold out forever for her, waiting for just one chance, though he knows he'll never see it. King was irrevocably, irreversibly, madly in love. But so was she, just with someone else.