tanya left karan because nandini wana marry her with other guy she didn't leave karan just for nandini's sake .and after few days she came back and said i cant live without bhoomi.and tanya used bhoomi against nandini.
actually tanya never used bhoomi but the whole family got her and karan married cuz nandani was in a coma and bhoomi was attached to tanya. she even left the house when nandani came home from the hospital. tanya was pretty good and sensible in those days remember. i don't like her character now but i also thought it unfair of bhoomi to accuse her. she really does love bhoomi.