If this were just a relatively short time ago in history, you would HAVE TO marry her.
In my opinion, once the two of you decided to have a baby, you in effect committed to at least an 18 year partnership. Also, if you want to automatically be legally your child's father, you need to be married. Otherwise, you'd have to go through the court system to legally prove your paternity.
If you love each other enough to purposefully have a child, you are in love enough to be married.
When I see people saying to a couple in your situation that they should wait to make sure, blah, blah, blah, it seems like it is disrespecting the future baby. It's as if they are saying that it's ok to plan a baby on a whim, but to be
married takes more thought and is a bigger decision.
BALONEY!
It is selfish to purposefully have a baby and not be married, in my opinion. Why have that poor kid born illegitimate, ON PURPOSE? It's like throwing an obstacle in front of him or her before they even get started.
Also, imarriage shows respect to your girlfriend and her family. Otherwise she would have to bear the stigma of being an unwed mother, and that stigma also effects her family. Whether or not that stigma is fair is irrelevant. The point is it exists, and it's better to not have that burden in the first place.