If Erik never imagined bunking down in the back of the Blackbird, of all places, he's been even less likely to imagine bunking down in the back of the Blackbird with Charles Xavier. There's barely enough room for one person on this small mattress, nevermind the two of them, but somehow they've made it work. He's not at all sure how, any more than he's ever been able to figure out how Charles could bend like that in the car fifty years ago, head practically in Erik's lap as Erik tried to drive. (It helped, perhaps, that Erik didn't need to keep his hands on the wheel.)
Charles has always slept on Erik, before Cuba and after. Every time Charles nods off when they're together, he ends up with his head on Erik's shoulder, Erik's lap, Erik's stomach. He's never seemed to realize how bad an idea it is, how vulnerable it makes him. Even now, Erik can't reciprocate, can't fall asleep until he's certain Charles is out completely; even now, the slightest stirring from Charles will bring Erik awake again in a moment, old instincts never quieted even for him.
After Alkali Lake, part of Erik assumed this would never happen again, that Charles would finally be done with him. After Charles died, he knew it wouldn't, that all their chances were lost. Yet here they are, Charles' head already putting Erik's arm to sleep. There's nowhere Erik would rather be, no one he would rather have by his side in the battles left to come.
"Stop brooding and go to sleep," Charles murmurs, which he must know will keep Erik up at least another quarter of an hour—but he's smiling as he says it, the way he always smiles when Erik's thought something he wants to hear.
"Stop eavesdropping and I might," Erik says, and if, before he finally drifts off, he thinks about how he's never felt as comfortable or at home in any bed twice this size unless Charles was in it next to him, Charles doesn't have a word to say about it.