It was on AO3 I believe,
Basically Steve and Darcy have been dating for a while when a still recovering Buck and Steve have a big fight.
Steve decided to leave for a while and goes to a cabin Tony owns up state in the mountains.
After he leaves Darcy finds out she's pregnant, but decides not to tell Steve for now, not wanting to pressure him into returning.
In Steve's absence Bucky steps up taking care of Darcy, which actually helps in his recovery.
The story follows Darcy through her pregnancy and eventually her going up to visit Steve.
Any help would be much appreciated!