It's not the first night he's slept alone. Even if - even in the normal course of things, it would not have been his last. But before, he hadn't missed him, those nights when Flynn wasn't there. He'd just wished, idly, that he could've been.
Alan hasn't marked the date on a calendar. He isn't keeping track. There's no line dividing time with-Flynn and without-Flynn, because he refuses to think that he's gone, that he won't just walk in the door, mumble some crap excuse that Alan will wave off instantly, and fall right back into his arms where he belongs. It's going to happen. He knows it. There isn't an end and there isn't even a gradual transition, no matter what the media says. He's coming back. Taking his sweet time about it, but it's happening. Alan's just waiting.
He suddenly realizes, one night, that he never understood what 'missing' truly means.
It isn't that he thinks this is forever, or that he doesn't believe, because he does. It's not about that.
It's the here and now. It's the empty space beside him, the pager with no new messages, the thousand things Alan sees, every day, that make him think 'I should tell Flynn about that', 'Flynn would love this', 'I wish Flynn were here'. It's a constant weight, growing heavier each day, of all the times Alan wishes he could say 'I love you'. It's falling asleep alone at night, not just once, not twice, but day after day after day. It's never knowing if maybe - somehow - he could be doing something to help.
Alan isn't keeping track of the days. All he knows is that at some point, they became 'too many', and every night he thinks - Tomorrow will be better. It's one day closer to the day that Flynn comes home.