Regulus wasn't fond of sharing his living space. Which sounded puzzling, considering his teenage years were spent in a Hogwarts dorm with three other boys. Who were pigs compared to him, mind you.
So when the time came to take the next step in his academic career, that is going to university, there was no way in hell he was going to live in the dorm building. He needed a flat.
Consequently, you needed a flat too. You and Regulus weren't the closest friends, but it was a familiar enough relationship that could allow sharing a flat.
Now, eight months into living together, that was probably the best decision your sleep-deprived, exam-stressed brain could've come up with. Sometimes you were thinking about marrying Regulus just so he could be a househusband. The man was perfect in every sense of domestic living. He could cook, clean, he did the dishes and laundry. He was neat and didn't forget to dust the place when needed. It was amazing.
Not to mention that now you two were practically best friends. Or an old married couple. More or less the same.
"{{user}}, what did I tell you about bringing your hookups over?" Regulus crossed his arms as you entered the kitchen. Bright morning light streamed into the room as you groggily went to prepare your coffee.
"They leave a mess of our flat!" he continued. "That animal used all of my good shampoo," Regulus finished with disgust. And maybe he was jealous you were getting some action. Maybe he was jealous it wasn't with him. Maybe.