The fanfic is a a/b/o with Tony as an alpha and Clint as a omega. They are in an established relationship.
Here are the details i remember:
The story starts out with Tony admiring his omega and something about a sky. So Tony starts waking up Clint and trying to get Clint to stay in bed with him.Tony doesn't have work that day so he jump start Clint heat.It talks about the alphas saliva making omegas go into heat. At first Clint doesn't want to because he has to go into work, but Tony wants to spend the day in bed so Clint eventually agrees.