I'm not going to say I know so much from personal experience,but I do know of a four year relationship that did break for similiar reasoning. The couple decided to part ways and try out their independence when things became too stuffy and repetitive. Plus ,they've only been with each other in life. And in their doing so,one found someone else. This happens and its ok becuase hearts change. It's very serious ,very emotional.Its rough to have a high school relationship go successful once your graduated h.S because a serious relationship in high school restricts alot of things you could be experiencing,but can't because of your die hard commitment to your mate. It is normal to have a few different relations before marriage when you are single and young,and for some its normal to stay with one person and never know what it's like to experience others. But if you are experiencing those feelings,and arent feeling too happy,maybe you havent exactly done your share of maturing and experiencing to complete you, before you seal the deal. Try to organize what it is you really seek.You also have to find out is it hormones? Or just the pre-marital jitters? Fear of commitment? I mean if your mate just isn't doing it for you,then your due for a reality check. Whats made you go on for so long? Think about how much you love this girl,is she everything you want? Think about if she has the ability to make you happy,does she wish to keep doing so? Is she really the one? Does she love you greatly? If so,maybe this is right decision to stay in your relationship. You decide. If these feelings of drifting strongly persist and you are still in confusion,i'd say discuss a possible break with your partner,a short break to clear your mind. From there maybe find out what direction you wish to pursue.