I married Mjoll and got sick of Aerin always being there in my house in Whiterun whenever I wasn't around. So I followed him as he appeared to be heading back to Riften. Once he got to the river/bridge just past the meadry, I sniped him in the back of the head and set his body floating down the river. Problem solved.
Just don't let Mjoll see you doing it, she doesn't react well and after that doesn't want anything to do with you anymore regardless that your married.

