just my 2 cents, if she "told" you murag out of curiousity lang to niya. talk with her about it and ask her what if ikaw ang naay laing ka date, how would she react. if she feels bad about it then tell her to stop kay mao na imo na feel karon. if dili gyud cya mo stop then there is a problem.
But if you "discovered" the dating then she only "told" you after confronting with her, then that is a BIG problem. Goodluck!