Regulus never thought he'd be feeling like this. Regulus wasn't for love. His parents weren't a product of love, his brother and him weren't, and he had never truly seen the prime example of love before his eyes. For a true while, he believed it didn't exist. That it was one of those fairytales parents told their children to get them through the week as still pure and innocent, like Santa Claus, or the tooth fairy. All things that were imaginary to bring comfort.
That was his idea of love.
Not what he was feeling. Not you, a girl he met through his brother when he was a mere boy, always swearing he disliked your every move, sneering at your name, but it was all an act. In fact, he'd snap up at the mere mention of you, defend your name (which he had to rarely do, as you were just a sweetheart to everyone), watch you from afar, silently pining — or whatever they called it in those Muggle movies he knew you had such a fond thing for.
And when he finally confessed after years, you two got together. Then, he decided he believed in love. But he had to go and spoil it like he did with everything he got his grimy little fingers on. Regulus had to go and be what his father wanted him to be, had to be mean to you like you weren't a literal doll in human form, and he ruined it all. Yet, he always crawled back to you. He heard you in every tune, saw you in every book, thought about you whenever he had a few — whenever he was going to sleep, whenever he woke up, every thing he did, you were in it.
Perhaps he was too busy being yours to think about someone else, but he had already planned out his entire life with you. Now, all he had to do was crawl back to you, and silently pine. Again.