i kow my father's girlfriend what should i do?

you just forget her . its a right way .

talk to your father. Let him know that you are aware of what he is doing, and point out the importance of all the diseases that are out there....if nothing is done, you should talk to your mom. She should be alerted, not only that her husband is cheating on her, but to have herself checked by a doctor. Good luck with this one....it is very hard to see your mom hurt, but in the long run, it would be the best thing for her.....NOT YOUR CHEATING FATHER.....

Nothing. You are better off pretending that you don't know her, that way they won't drag you into any relationship problems they may have.

Whats wrong with that?

is your father still married? if so then i would consider talking with him about it.

ask him whether she has a daughter to make her ur gf

Why would you want to do anything?