| | Man, I've been there
When I graduated I was in a relationship that lasted 5 years. All along the way I questioned whether or not this was right for me. She also claimed that I was all she had so the thought of leaving would be a hit on my concious. The truth is the longer you wait, the worse it is going to be. If she is two years younger than you that will give her about two years of high school left but if you wait until she graduates, you've added to her pain by robbing her of her of the opportunity of expierencing a normal high school life. The one thing that I concluded is that at 18, I should've been in a serious relationship. The best thing to do is to be honest with yourself and really understand what you want. Then understand what you need to do in order to get what you want. If being in a relationship is hurting your progress than you know what you need to do. Do it and be prepared to live with your decision.