Not sure what to think about my Girlfriend joining a sorority?

This is from experience - you guys are at a very transitional point in your lives right now. It sounds like high school has just ended and you both shared a pretty good high school relationship with one another.

However, this is really the point in life when A LOT of people start changing. Sometimes for the better, sometimes for the worse. This is caused by a lot of different factors working together. When people go off to college, they are usually thrown into a foreign environment with a new set of people. They make choices and decisions they wouldn't normally make in an attempt to fit in with everyone, because no one wants to be in a new environment alone or without friends. They start making new friends, they start trying new things, and they really start discovering themselves. So there is a good chance her new friends will be strongly influencing her to drink and she may give in due to the desire to fit in with everyone else.

I graduated college a year ago. Some of my friends from high school have not changed a bit. Some are completely different people now. Some of those who have changed are better, more interesting people, and some of them are terrible people who've dropped a lot of their qualities about them. Those friends got weeded out.

I don't want to burst your bubble but I'm going to be honest, all of the long term high school relationships I saw go into college (some of these were 4+ year relationships since freshman year) failed MISERABLY. The distance, the temptations, the changes, the parties, the new friends, the drinking - all are a recipe for failure. All my friends either got cheated on by their girlfriends, or cheated on their girlfriends. I can already tell based on the way you've described your situation that you probably will be one of those people who will hold onto who they are mostly through college and not change much, and your girlfriend's fate is really in the friend group she decides to go with at school. Don't mold yourself for her, and don't make her mold herself for you. Be who you are and believe in your core values. And at one point, even if you two do move forward into college, she may want to be single during her college experience. And believe me, girls, no matter how sweet or innocent or trusting - all of them are capable of making horrible mistakes when drunk or under peer pressure.

I was lucky enough to have my high school girlfriend dump me before college because she knew all the above was true, and I spent most of my college life single. Which is probably the smartest thing to do.

Don't hold her back from doing something that will most likely be the best thing that she will do during her college career. If you really trust her, what are you worried about?