You can contract the HPV virus from skin to skin contact, does not have to be vaginal sex. There is no way to pin point time frames regarding when you did get it. I am married and found out after 16 years of marriage (monogamous) that I had HPV------so don't automatically assume she is cheating. Check out the Center for Disease Control for more information on HPV. Good luck!
Since it's passes skin to skin, who's to say what skin? People can carry the virus in their mouths/throats, so of course you can get it from oral. And you could have easily gotten it from you own hands, having touched these other girl's genitals (I assume you touched each other, not just straight to oral, right?) or from their hands.
Anyway, you definitely can get it other ways than just intercourse. This is no indication at all that your gf cheated.