@APPY,
What if you did not know that your girlfriend had sex with six other dudes the month before and those other dudes had AIDS, herpes or some other sexually transmitted disease? Is there a chance that you'd get AIDS or herpes even though you did not ejaculate in her and had masterbated the day before?
You betcha! Start thinking about protecting your own health, dude. Those condoms aren't just for pregnancy prevention.