1. It's always right there after she leaves, a steady light in the dark reminding you that you're not actually dead. She once thought it was funny to put a reactor in a tidy little display box to prove you had a heart. Now you're using it as proof again: proof that your heart is here, and beating, and not in her pocket in a taxi on the way to the airport.
2. In the midst of a truly epic hangover, it is the only light source you can stand.
3. At four in the morning when you're rewiring a remote control on the balcony because you can't sleep but don't have the energy to go all the way down to the lab, it's just enough light to see what you're doing by. Jarvis disagrees. He informs you that it will be difficult to fit a pair of bifocals under the suit's helmet. You inform him that he's free to go eat a bag of dicks. The remote gets tossed into the ocean.
4. When you don't have a table to tap your fingers on impatiently, the casing makes an adequate substitute, just noisy enough to draw the attention of the rest of the team. The speaker frowns and asks if you're bored. Of course not, you tell him, you always listen raptly when your elders speak. Note to self: old guy jokes are getting stale. Have Jarvis research the 1940s for new material.
5. You get shot down over the bay and sink deep, deep down, repulsors failing and air filtration system at 19%. That small glow illuminates the murky water rushing past, then a red-gloved hand reaching out for you. When you're both dragged onto the shore and gasping in fresh air, he says he wouldn't have found you without that light to follow.
6. After you kiss him for the first time, the faint blue through your t-shirt reflects in his wide eyes, and it's one of the funniest things you've ever seen.
7. He shows you how to make shadow puppets. So this is what people did for fun before cable TV.
8. He sleeps less than you do, if that's possible, and you wake sometimes to catch him reading a paperback by the light of your chest. You tell him you're not a book light, but he shushes you because Inigo is fighting the six-fingered man. You come to a compromise: he reads the rest aloud by arc reactor light. You don't really give two shits about The Princess Bride, but he could read the manual for one of Hammer's missile launchers to you and you'd love it.
9. It's exactly the right amount of light for lying awake alone with your thoughts in an empty bed, panicking silently over asking your boyfriend (and four closest superfriends) to move in with you.
10. When he comes to bed smelling like a late night at the gym, he never bothers turning on a light or letting his eyes adjust. He follows the glow to you. He'll always follow it to you, he says as he curls himself around you, until it goes out.
He eclipses the light with one warm hand. You let him. You don't need the proof anymore.