should I feel Disappointed or not?

I don really like this feeling and I hardly have this disappoint feeling.
We are friends at the first day of orientation, I go towards her to know her because I saw her sitting alone behind me, so I invited her to sat beside with me, and that time Sarah haven't reach yet. So we have know each other for one month plus, yet slowly I don't really understand what she's doing at all?! Sometime act like this sometime like that. aiyo~~~ Fan ar... I can tell she is a nice girl, just not yet grown up, so I always tell myself not to judge her in that sense, because is not fair anyway. I also have this problem before when I was in secondary school, until I went for National Service and study nursing course improve me a lot in many ways. I just hope one day I can tell her my feelings if not I will burst, but I don't have the guts to tell her. Even I have hard time to tell my BF my inner feelings. For all this year, I don't really tell my true feelings out, people can say I'm a happy and cheerful girl, yet deep inside hinder many unknown feelings. Only one Whom I trust is God, because He's the one only know my inner feeling more than any other people. I pray that god show me the way and provide me guidance, to become nurse must to build up critical thinking and making decision on the spot, I don't even have the confidence in this area. I know I have weakness in this areas. Aiyaya~~