Nnoooooo, just a random girl that he sleeps with, started a comic company with and spends all his time with. Really, it could be confused with a "friend with benefits" situation, but yes, Sarah is Kevin's girlfriend.
That has to be the single greatest mutant super power ever! It would revolutionize the world for all of us who feel too lazy to just get up and pee. I wouldn't have to worry about trying not to explode during exams because there are no bathroom passes allowed! I could just make someone else have to pee!