Lots of studying

Over the weekend I studied a lot for school. We had again some exams coming up, and my grades seemed slipping. I could not concentrate much, was always thinking about B. Fortunately C was not there on Friday evening, at K's party.
The good mood that had come last Thursday was only short lived. I am back again in deep depression, everything is senseless. I do not know what to do, how to move forward. Whad should I do regarding B? How can I avoid C's approaches and advances? I am stuck between these two, just am somehow not adjusted to reality.