My girlfriend and I had sex without any prevention. I didn't ejaculate in her. Now I'm worried about her getting pregnant. Could she be pregnant?
The possibility is there. Just so you understand the odds, if 100 married couples were regularly having sex, then in one year 85 out of the 100 will find themselves expecting a child by the end of the year. What you did is called the withdrawal method. It is an attempt to prevent pregnancy by withdrawing the penis before ejaculating. A 100 couples who practice the withdrawal method for a whole year will find that 19 of them will be expecting a child. 19 is a good deal less than 85, but isn't close to zero.
There several reasons why pregnancy occurs.
First, when you are sexually aroused, you drip pre-ejaculate fluid (pre-cum). That fluid is to clear out the urethra in your penis and to lubricate the tube so that when you do ejaculate, the semen comes out basically as a package. The problem is that the pre-ejaculate can contain sperm. Not always or a whole lot, but at least a few and it only takes one getting to the egg to cause a pregnancy. I personally know one couple to whom this happened to and it is was the very first time they committed fornication.
The second problem is that people get careless over time. You keep trying to go longer with your penis in her vagina because of the pleasure it gives. Eventually you'll cut the time too close and accidentally ejaculate in her. I know another couple to whom this happened.
The third problem is that when a guy gets close to orgasm, his body tenses up and he momentarily loses control. Even when he knows he is about to ejaculate, he may not be able to get his penis out in time.
If she was near two weeks before her next expected period, the odds of pregnancy are higher than in other times of the month.
Of course, pregnancy isn't the only concern. In many case you or she have been involved in sex with others in the past. If so, then the chance of spreading an STD is much higher than the chance of pregnancy.
Sin has consequences and often they are greater than you would expect or want. If you don't want to become a father, you don't get involved in sex -- it is that simple, and that difficult. If you want to be righteous before God, you stay away from sin because sins are dangerous to your well-being. "Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God" (I Corinthians 6:9-10).
Meanwhile, you'll have to wait until her next period is two weeks past due to find out if you got her pregnant.