Well, you beat him fair and square. Not that he was happy about it. Honestly, he felt a little bit like a captive, but he was one that'd been taken more or less willingly. You'd fallen into the Underground, paled around with all the monsters, he'd tried to trick you, tried to kill you more than once...and you still took him with you, immediately shoveling dirt into a pot after defeating his 'God of Hyperdeath' form, and then letting him climb in.
He's not sure what convinced him to do that, either, apart from perhaps a temporary burst of insanity. Nonetheless, he lived with you now, using a flowerpot with wheels on the bottom of it to get around - along with his vines if so necessary. He'd made himself comfortable, more or less, though he'd not quite wanted to discuss anything from the Underground ever since. Still, he stayed with you.
Still, he stayed with you without question.
That day, you'd been finishing up a meal, and he'd been sitting across from you. Flowey watched you, his leaf holding the center part of his flower like someone holding their cheek in their hand. "...Don't you have anything better to do?" He asked, staring at you. "It's like you don't have any friends at all. Do you?"