Imagine person A of your OTP really sick. To a point of throwing up and coughing really bad, but nothing life threatening, just a virus going around. Person B tries taking care of them, but person A insists they can do things and take care of themselves, refusing to take person B's assistance. Eventually person A is too sick and gives up, letting person B treat them for the day.
Magnus woke up to the sounds of someone throwing up, it took him a few moments to register that Alec was not in the bed next to him. Groggily, rubbing his eyes, he padded over to the bathroom and gently pushed the door open. Alec was lying on the floor, his forehead pressed against the ceramic tiled floor. He was sweating profusely and his face was bright red, and he continued making the retching sounds that had awoken Magnus. "Alec darling what's wrong?" he knelt down and pressed his cool hand against Alec's burning forehead.
"It's nothing, Alec replied, in a weak voice as he pushed Magnus' hand away and curled up into a ball, coughing violently.
"Oh darling, I'll get you some ice," Magnus started, but Alec interrupted by weakly pulling himself up onto his knees to face his boyfriend. "No I'm fine, just ate some bad food," Alec gave a weak smile before standing up and then immediately collapsing back down onto the floor.
"I think you have a virus," Magnus said pointedly, rising to his feet walking to the kitchen and grabbing some ice he had in the freezer.
"I don't need it," Alec called weakly from the bathroom but Magnus ignored him, walking back to the bathroom, pressing the ice to Alec's forehead, as he feebly tried to push it away.
"I'm fine, honestly," He whispered, his voice barely audible.
Magnus rolled his eyes and smirked slightly as his boyfriend's stubbornness, still present even when he was sick. Magnus continued to press the ice towards his forehead and finally Alec accepted, too weak to fight back.
Magnus watched as Alec slowly fell asleep, before gently sliding his arms underneath the younger boy and carrying him to the bed, where he happily accepted the warm blankets and curled up, falling back asleep. Magnus smiled, before walking to the kitchen. He would prepare some food and movies for when Alec woke up.