There are millions of little microscopic sperm in one ejaculation (unless he has a reason for low sperm count). So if you see semen coming out that is normal. But the Sperm travel very fast.
As far as you missing one BC pill, it is possible for you to get preggo, but only if it is the time of the month around ovulation time. I wouldn't lose too much sleep over it just yet. But if you do not want to get preggo, then be careful and REMEMBER your pills :)