This is set just after Kiss Kiss, Bang Bang. Doesn't go into details of where they are or anything, it's just something I thought of. Please let me know what you think!
Jack sat down on the bed beside Ianto. Ianto shifted away, trying not to make it too obvious. Jack raised a hand as if to pull him back, then let it drop.
"What's wrong?" Jack asked, sounding upset.
"Nothing," Ianto shrugged. "Who says anything's wrong?"
"I know you well enough by now to tell when something's bothering you," Jack said, moving closer. "What is it?"
"Something you said in that office, before John showed up." Ianto hesitated, unsure about continuing. He'd thought it out before and it still sounded incredibly whiny. But he couldn't hide it – it was bothering him and Jack wouldn't shut up until he found out what it was. "You said he was a reminder of your past and you wanted him gone."
"And what if I show up, sometime in the future, and I'm just a reminder too? Are you going to want me gone, just like that?" Ianto turned to Jack and rode over his protests. "When you haven't seen me in years but you've moved on so far you won't even want to catch up? Just give me what I want and tell me to shove off?"
"He reminds me of a past where I was someone else, someone that I don't… Don't want to be anymore. But who I am now… I won't mind being reminded of that in the future."
"I'd bet you thought that when you were that other person, too. You're immortal, Jack, I get that. And I'm not and I'm going to get old and die when you haven't aged a day. And you can't get tied down to people because it hurts too much when they go away and you're still there the same. I get that and I'm not expecting your eternal undying love or anything. But I just need to know that you're still going to at least like me when all this is gone. That you're not going to push me away from you because I remind you of something you don't like."
"John is… different. He's not you." That was all too obvious, and it brought up other pains that Ianto wouldn't speak of. "But I won't do that to you, Ianto. I promise. I'll always be glad to see you." Jack's stare was piercing and Ianto looked away, unable to meet his gaze. Somehow the reassurances felt empty. How could Jack make promises about how he'd feel decades in the future? Ianto knew there were no promises, no truths that would take away the worry about what would happen. It was just one of the consequences of being with Jack; that the future was going to be so different for each of them.
He just had to figure out if the consequences later were worth what they had together now.