teacake: Yes, but in "Endgame" it was revealed that Seven was married to Chakotay for three years until she died. So she wasn't just trying out love on him.
Guy Gardener: Perhaps the "Natural Law" episode had something to do with it but I don't think it would have happened so late in the series. By that time, she would have thought of Chakotay as a coworker and their relationship would have already been defined. It's very unlikely she would consider him relationship material.
Who knows why she picked him for her simulation in "Human Error" because in "Someone to Watch Over Me", he wasn't on the list. (I guess at that time the Janeway/Chakotay relationship was still on the writer's table.