"Let's just stay in bed a little bit longer," Tony suggested.
"I need to go for my morning run," Steve answered.
"Skip it. Please! For me," Tony pleaded, "It's not often that I actually want to have a lazy morning."
"Hmm.... You do make a valid argument," Steve pretended to consider, "For you I will skip my morning run and I will have a lazy Sunday morning with you."
"Yayy," Tony yawned, "Sleep now. Fun later."
Steve rolled his eyes with a fond smile curving his lips but they were both soon asleep curled up together in each others arms.
*1 hour later*
"I just want to be lazy," Tony groaned.
"You can," Steve replied, "It's Sunday. You don't have any meetings and JARVIS is keeping an eye on the bots in the lab."
"I love you," Tony murmured, "You understand me."
"I love you too," Steve smiled, "You're patient with me and you're always willing to help me get used to the 21st century."
They both smiled softly while staring into each others eyes before they kissed lazily for a minute.
This would become their new Sunday tradition. Every Sunday they would stay in bed staring into each others eyes and professing their love to each other while trading lazy kisses. This was their new Sunday and they loved it.
They're happy with their life and they would never change a thing about the family unit they'd built with the Avengers and they would never change a thing about their relationship. Until they were ready for marriage, then their relationship would change slightly but only slightly.
They were complete.