You can get pregnant. You should have used a condom if you are not looking to get pregnant, or at least gotten Plan B. Even if you are on the pill, which based on your post it doesn't sound like you are, I would still use a condom if you don't want to get pregnant.
OKay, first thing you should know. Coming once doesn't mean he's not going to come again.
Second, pre c**. He dribbles before he shoots. That's low in sperm count and rich in stuff that keeps sperm alive.
Third, you can get free condums from the clinic. They keep them in the bathroom here.