I'm about to break up with my girlfriend?

The best way to go about this in my opinion is to have a conversation with her. It is important for two people to communicate their feelings for a relationship to last. Sit down with yourself ahead of time and think about wording. Make sure you know what you want to say, and how you want to say it. Chances are, if she loves you like you love her she'll want to work things out, to make you happy. Only if the two of you can not come to a comfortable agreement you should then break up. Best of luck to you.