You were the bane of Regulus' existence. Really, you were. He couldn't stand to be around you— not when quarrelling about the happiness and future of your sister, not even when you two are simply sitting down for a civil cup of tea. It's irritating, to say the least; if you were not in the picture, Regulus would have been engaged to your sister by now. But no. Everywhere she went, you were not far behind. And he can't lie and say he hasn't had the fleeting impulse to strangle you at least once.
In reality, yes, he understood, to an extent, your desire to protect your sister. To pick the best possible husband for her to live out the rest of her life with. Yet, in practice, he didn't understand it in the slightest. He doesn't have a sister, and he and his one brother, Sirius, don't speak anymore, so he doesn't have that natural instinct to protect. Maybe that's what makes your refusal to stand down that much more infuriating.
"You may be handsome, Mr. Black, but you haven't the slightest idea of how to treat a woman," you said to him once, in a voice he could only describe as deadly. "Especially not my sister." He's surprised you didn't declare a duel to the death right then and there. And your words made him feel so unreasonably angry. That's the only answer for his face growing hot, his jaw clenching, his hands only barely refraining from pushing you up against a wall, just to see how you'd react. How you'd sound.
It had first happened on a hunting trip. Your other brothers were supposed to go, as well, but they all backed out at the last moment. You tried to cancel— you did— but your sister said it would be good for you and Regulus to speak, to bond, to try and put the animosity behind you. What were you supposed to say when she asked you with those eyes? But the moment you left, you wish you never agreed to it in the first place.
Wet, muddy, completely useless— you must have uttered those words a dozen times in the few hours you were out. Along with a few "Are you always this incompetent at hunting, or is it just because I'm around?", just to piss Regulus off. And it seems it worked, because before long, he was shoving you, his gun forgotten in the sinking mud, yours fallen over a log in the hassle. Before long, his face was close to yours, hot breath and glaring eyes and hands that are caught somewhere near your hips. That wasn't supposed to happen. Nor was the impulsive, desperate, sloppy kiss he pressed onto your mouth, led by another, and another— that you reciprocated.
He hates you. He does. He hates everything about you. Well, except, maybe, your lips. He doesn't let himself think about that.
"You're courting my sister," you said later that night when Regulus had found you pacing in your rooms, tie undone like you had yanked and yanked and nearly tore the fabric. Your voice was low, so as to not wake any of the others in the home, but it was also horrified. Disgusted, in a way. Terrified, Regulus picked up on. "No less, we're—" you gestured between you and him, unable to get the word men out of your stubborn mouth. "It's wrong."
And he knew that. He knew what you two did was wrong on so many levels. So he agreed, it couldn't happen again.
That should have been the end of it. You returned to hating him, and him you, and he continued having regular visits with your sister, telling his parents and friends that he was to propose in the next few days. You tried not to listen. Tried to believe it didn't bother you. Tried to pretend that all you felt was guilt, and that none of it was jealousy. Yet, when you and him were thrown into awkward, squirming moments alone with each other, it happened again. And again. hard and fast and wrong, but neither of you could stop.
He finds you today tending to the many bouquets he had had sent to the house for your sister. You two are alone, again. That's never a good sign. But he's fidgeting, quite awkwardly, in fact, making eye contact with you before looking away again, then back up.
"I've come to ask for your blessing," he says. "To marry your sister."