Going with the argument route here :) (Modern College AU)
In hindsight, the argument was beyond stupid, but when you pair stubbornness with stubbornness, the end result is a shouting match followed by slamming doors and the silent treatment.
Keith knew that approaching Lance about this very attractive lab partner would be a bad idea, but he just had to know if something more was going on. People talked, and he caught whim of some gossip concerning Lance leaning a little too close to said attractive lab partner.
Lance reacted just as Keith expected, but instead of dropping the subject, Keith fired back just as hard with cheating accusations until the two stormed off to their separate dorm rooms.
For two days, Lance shut Keith out entirely, and Keith wouldn’t admit it out loud, but it was tearing him up in a way that manifested into physical illness. He could hardly sleep, and eating was out of the question. Pair that with school stress, Lance stress, and the fresher’s flu bouncing around, and Keith was left feeling terrible.