Have Relationship Questions? Ask a Counselor for Answers ASAP
When partners have been together for some time, they become complacent/used to each other (which is not necessarily a bad thing) To some this is comforting, to others (like in her case it seems that she may be still expecting the sparks initially felt when people start dating) The two of you had also gotten together when you were young and perhaps she is wanting to explore other options of what you had mentioned there is a possibility of another guy.
No matter what you decide to do (stay or go) she will make her decision most likely independently of your actions. You may get hurt if you stay.