This is the way it happens: Standing on tiptoe to kiss your boyfriend is shockingly girly, and Seamus is small, so he cajoles, or flirts, or jumps, or sits on the lap, or otherwise tackles so that Dean comes down to him--not to his level, really, as they have always been on the same level, but so that he is within striking distance.
Then he uses his entire body to make sure that Dean is paying full and appropriate attention to the proceedings. Dean occasionally escapes into his head, into the art, into that space that isn't really on the Earth, but sex is about the body, about the now, about being fully present. Seamus reckons that is his role in Dean's life, to keep him from floating off into the aether. Oddly, at school it was the other way round.
Dean's cock is long and slender, which Seamus thinks is perfect for fucking, while his own is shorter and thicker, perfect for sucking, so that is usually the scenario. Change can be good, sure, but Seamus likes things to have the best use for their form. Besides, Dean's lips are amazing, and Seamus's arse is amazing, so who would argue with that? Seamus wanks to the memory of his cock sliding in and out of Dean's full lips, or to the way Dean's dark, long fingers sink into the flesh of his pale thighs as he pulls Seamus on and off his own cock.
And after, when they are in a sweaty pile on the bed, or the couch, or the kitchen floor, or the model platform in the studio, Seamus pushes his floppy fringe out of his eyes and burrows into Dean's chest, or Dean lays his head on Seamus. And then they kiss, because when they are laying together everything is within reach.