Disclaimer: If the Potterverse was mine, things would have gone very differently. That said, many thanks to JK Rowling for letting us play in the world she created. It's one hell of a sandbox.
"WHOMP!"
"Just like that, you're not coming back?" Seamus barked as he threw his school books into his trunk.
Dean sighed. "You know it's not going to be safe for muggleborns. I wouldn't be surprised if Harry keeps Hermione from coming back too."
"THUD!"
"But it won't be safe for you out there either!" Seamus challenged, dragging his trunk to the floor.
"You think I don't know that?" Dean growled. "But I've got a better shot at avoiding whatever's coming if I'm not holed up in a castle where I'm supposed to be."
"SLAM!"
Seamus dropped the lid of his trunk and, full of frustration, turned to face his roommate and best friend.
"I'm about to sound like a bloody bird, so don't ever tell anyone I said this- you're my best friend and I feel like you're abandoning me. Mum watches this muggle telly program called "Grey's Anemone"-
"Anatomy," Dean corrected
The Irishman rolled his eyes. "Whatever. Anyway, these birds talk about being each other's 'person'. It's kind of like…"
"Like you're cosmically bound, best friends, partners in crime, and have complete trust in each other?" Dean supplied carefully. The word "soulmate", though left unsaid, hung in the air.
"CRASH!"
Needing to dispel the intensity of the moment, Seamus flopped heavily onto his bed, his headboard colliding with the stone wall.
"Exactly. Mate, are you watching chick programs now? Anyway, I just think you're going to leave and find someone better than me. And then I'll be person-less, which would be complete shite," he muttered, flushing with embarrassment at having laid his emotions out in the open.
"SMACK!"
Dean's only immediate response was a face-palm.
"Why do you think I've been your partner in literally every class since day one, even though you blow shit up every term?" he asked incredulously. "We're best mates, practically attached at the hip even outside of class, and you're worried I'm going to leave you? Merlin, you're an idiot. We're in this together, forever. I've always been your person, and I'm going to keep being your person. I'm just going to have to do it from a distance for a bit," he finished, bringing them back to the reality of their situation.
Seamus swallowed the lump in his throat. He'd always felt a little more for his "person" than was probably acceptable for mates or even brothers, and he'd not had the time or opportunity to suss it all out. With so much left unsaid, the idea that this could be the last time they ever saw each other was tearing him apart.
"CRACK!"
He pulled Dean into a quickly reciprocated bone crushing hug.
"Promise me you'll be careful," he choked out. There, that was masculine yet heartfelt. Perfectly acceptable final words.
Dean, however, could read him like an open book. "I'll come back to you, mate. I promise."