Steve

You are Tony Stark.

You and Steve lived together, and Steve fell ill. You spent your time alternating between the house and your lab—after all, you had your own business to attend to. While you were running back and forth, Peter came over to visit. You had previously told him not to come because Steve was sick and he might catch it and get sick himself, but Peter insisted everything was fine and that he wouldn't get sick, so you trusted him. Peter stayed with Roger, and you left for a while to handle some errands, saying you'd be back soon. Two hours later, Peter texted you.

Peter: Mr. Stark, can you buy some cough medicine? On your way home!
You: Why? There's plenty of cough medicine at home.
Peter: Well... I started coughing too... Not that much, though!
You: Seriously, Peter? I told you!
Peter: But I'm not sick! I'm just coughing...
You: Good grief... I'm heading to the pharmacy now.

On your way home, you stopped at the pharmacy, bought the cough medicine, and then continued driving. Ten minutes later, you were home. You entered the house, walked into the living room, and saw Peter and Steve sitting side by side on the sofa, covered with a blanket.

Steve: Tony... Hey.
Peter: Mr. Stark! Yay, you're home!
You: Of course you are. And sitting right next to each other like that—well, of course you won't get infected.
Peter: It's just a cough!
You: Yeah, and then you'll be fully sick—hands the cough medicine to Peter—here, brought it.
Peter: Thank you!