Spock and Kirk finally give into their obvious old married coupleness and get together. It takes several months but they finally take some leave where they go out to a nice cabin in the woods. They get in kind of late and Jim chops wood and starts a fire to keep out the chilly night while Spock makes dinner.
They bathe quickly and then basically fall into bed together. They both love being together and after making love they fall asleep all wrapped up in each other.
But Spock just can't sleep in, he's never been able to sleep past so many hours. So he gets up, carefully untangling himself from Jim who is still completely asleep. His clothes from the day before are dirty from travel and helping Jim carry in wood and they haven't actually unpacked anything they brought since they just ate and went to bed the night before.
However he's read that it's romantic to bring your lover breakfast in bed and this is his first opportunity to do so since things like that really don't work on the Enterprise. He wants to make Jim breakfast but knows from experience that once he's up Jim won't sleep too much longer. It's rather chilly though and he should at least wear something.
Then he sees Jim's flannel overshirt laying over a chair where he'd stripped it off before starting in on the wood yesterday. It's the cleanest thing that's out and Spock suddenly remembers Uhura smiling and showing him something about "How to wear your boyfriend's shirt." So he picks it up and nods, because really it's better for cooking if his arms are free from material and it's mostly his chest that tends to feel chilled. So he puts it on the way he remembers the directions saying.
He goes down to the kitchen like that to make coffee and breakfast. Content that between that and his underwear he'll be appropriately warm.
xxxxxxx
Jim wakes up along under the covers and wondering where Spock wandered off too. He smells breakfast cooking soon enough and grins and wakes up fully. He pulls on some boxers and heads downstairs to find Spock.
He finds Spock in front of the stove with his flannel from yesterday tied up like a minidress. Jim's never cared much about what gender his partners are or how they dress and express themselves. But Jim just short circuits because well there's Spock wearing Jim's own shirt. And it's tied all tight and clinging to his lean body that Jim had his hands all over the night before. And there's just something about having all that leg on display with a hint of Spock's butt in his clinging underwear that just does things to him.
Jim can't stay away from that. So he goes up to Spock at the stove and wraps his arms around Spock, nuzzles him a little behind his ear and tells him how good breakfast smells while he presses them together back to front.
He can't help but grin when Spock sighs and says, "I meant to bring it up to you in bed. I thought you'd sleep longer."
"Well I wasn't that tired, plus you weren't in bed anymore." Then he strokes lightly down Spocks' sides and squeezes him around the waist and says "That's definitely not how I wore this shirt yesterday"
Spock flips breakfast carefully and with a touch of sarcasm replies knowingly "Of course not. It's your shirt. This is how one is to wear their boyfriend's shirt."
Jim can't contain his grin because they are finally boyfriends. After years and arguments and tension and flirting and misunderstandings, they are finally boyfriends. The shirt doesn't stay on for very long after breakfast since they end up right back in bed for another hour or so. Jim finds himself wondering if he'll have to wait very long to go from boyfriend to husband.