Finding a private place at Hogwarts wasn't really as difficult as it might sound.Especially for Rodolphus and Bella, who could clear a room with a single look.
He found an alcove not too far away - his need too urgent to wait for his dorm to be clear, and of course he couldn't get into hers thanks to Dumbleasses' wards against male visitors. Perhaps he should have set a privacy spell of some sort, or even a concealment charm might have come in handy. But at that moment, his second brain had assumed command, and it was giving orders, those orders being touch her, touch her now.
He pressed her up against the wall, rather a daring move for young Rodolphus, at least with Bellatrix. He kissed her again, almost demandingly, his hands traveling over her body. Her breasts felt so firm and ripe beneath his hands as he caressed them. Later they would do this properly - in a bed and quite naked. Or at least on a flat surface. But for now this would have to do.