"I just don't want you staying over for movie night with Amber. She'll try to turn it into a bloody date at this rate," Dean answered with a laugh, seeing the hands-on-hips pose and lifting and eyebrow, amused. "If you want to stay over that's fine though. We could go out to see a movie or something, so my sister doesn't try to seduce you." He rolled his eyes, making a comically over-the-top face of disgust.
It did bother Dean, probably a bit more than it should considering that Dean really had no actual worry that Seamus would snog his sister. Some of it was over protective big-brother syndrome. Seamus WOULDN'T snog Amber, so she might end up all weepy over him. Which would put Dean in a spot, since he couldn't punch Seamus for it when it wasn't his fault, really. The rest was just a vague sort of odd possessiveness Dean had about Seamus. He was the child of a big family, the only things that were really his were magic, and Seamus, who was his mate first. He shared everything else, as needed, and he didn't mind it.
Mostly, it was just a bit weird to have your sister mooning over your mate, though. He felt a bit bad for Ron Weasley, really. Much as he tried not to think about Ginny having mooned over Harry.
Amber bounced back in - lip gloss newly applied, Dean noticed - and handed over a stack of towels. Dean started wiping up the water again as Amber flirted, and then chased her off, grabbing the shirt he'd pulled off to throw at Seamus and told Seamus to follow him, if he wanted to. He dumped the wet towels in the hamper on his way, and shut the door, calling to Amber to watch the kids as Dean went to dig through a drawer for a clean, and unsoaked or snotted-on shirt.
Dean did, at least, have his own room. It was small, and tended to double as a storage room, since there were boxes and such shoved in the closet and the corner of the room, but he didn't have to share with actual brothers, since Ross and Owen roomed together. It wasn't exactly tidy, but it wasn't a mess either, a few sketches and football posters tacked on the walls and his bigger sketchpad tossed onto the unmade bed earlier when he'd gone outside. "You want a shirt, or just dry out with a charm?" he asked, holding out a worn tee shirt in offering. Amber was probably still hovering in hopes they came back out.