Well, in that case, don't stick around just because of the kid. If you love her, stay with her. Otherwise, you can be a friend to her while she goes through the pregnancy or even end the relationship and duck and hide.
In the meantime, keep doing your thing (school, work, etc.). But expect her to come knocking on your door in nine months. You'll have some choices to make then, and you'll have to ponder what you want to do (it doesn't matter what I or anyone else would do). And I'm sure you know the options at that point.
That's all you can do. It's her body, and she can do what she chooses. All you can do is give your input and recommendations.
Do whatever the right thing is for you. No one said you have to stay with her or marry her. Depending on what she chooses, you may need to be involved as a father or just send the money and not be involved, or both.