Steve when you told him you were pregnant.
You and the Avengers were standing in Fury's office. Little did Steve know that you arranged the meeting to tell him about your pregnancy.
Everybody but Steve already knew about it. The 'meeting' was actually a surprise-party.
"Baby, this meeting isn't really a meeting."
He looked confused.
"We're going to be parents, Steve."
You said with the biggest smile.
At first you saw that Steve wanted to scream of happiness, but then he realised he was surrounded by the rest of the avengers and he held it in.
He just smiled at you, walked over to you and kissed you.