There were some things that Tony simply didn't need to know.

Steve had learned that fact rather quickly after he became acquainted with the genius. Tony had a small habit of abusing knowledge. Like how he blackmailed Clint with a picture of his drunken cross-dressing (something he did on a dare from Tony) or the fact that he still teased Natasha about tearing up at the end of Sophie's Choice. Even Pepper got some mocking for once mixing up an appointment date when she first started working as Tony's PA.

Whenever Tony caught on to something, however, it was almost impossible to get him off the trail. That was something else Steve had learned quickly. And that he was a little grateful for if he was being honest. If Tony was anything less than a stubborn ass, they wouldn't be together.

"Steve, why do you do that?"

"What?"

Steve looked away from his book and down at Tony. They were curled up in bed, Tony laying on his back with the blanket pooled at his waist, Steve sitting up reading by the light of the arc reactor. Or, at least, what light made it through his fingers.

"Put your hand on the reactor. You do it every night. I just wanted to know why."

Steve felt grateful for his training with Natasha; it was the only thing keeping him from stiffening. "I thought we talked about this?"

Tony sat up and leaned against Steve's shoulder, "Yeah. You said that you didn't like the light. It kept you awake, or something."

"So why ask again?"

"When I slept on my stomach, you still put your hand over my heart."

Sighing, Steve put his book aside. "I got used to the position, Tony. You keep making a big deal out of this."

Tony raised a skeptical eyebrow. "Maybe because I don't think it's habit. When I come up from the lab and you're asleep, you're not in that position, but you curl over and do it the second I lay down. Why?"

"I believe the term you used to describe my unconscious self was 'affectionate octopus.'"

Another skeptical look. Finally, Tony yawned and rolled over, saying, "I know you're lying, Puddin' Pop. One of these days, I'll know why."

Steve slumped. He knew it was true. One of these days he would have to tell Tony how worried he got about the arc reactor and the nightmares he had where someone, some no name enemy, ripped it out of Tony like Obadiah did those years ago. How sometimes, he woke in a cold sweat, thinking that he was holding a corpse, that Tony had died and left Steve alone to mourn another friend, another love, and the only thing that stopped the panic was the hum of the arc reactor, the warmth of the light under his fingers. But that time wasn't now. He didn't need to say anything yet.

There were simply somethings Tony didn't need to know.