Hi there.
You need some accurate information. First, what you precum is actually Cowper's Gland secretion. This happy little gland secretes a milky fluid prior to ejaculation. It MAY contain millions of sperm left over from a previous ejaculation. thus, coming into contact with your girlfriend's vagina, even without having an orgasm, can result in pregnancy. It's statistically unlikely, but not impossible.
So, use a condom if you're anywhere near her vagina, OK?