i think everyone focused only the situation but didnt find the problem.
both were taking care of each others
boy was serious in love but the girl was not (might be pretending and enjoying the time with him)
when the boy come up with serious emotion, girl replied that she loves him as a brother.
that means girl already know about the coming situation
if she told him with out taking any time, thats pre planned
if she told him after talking some time, thats considerable
if she told him after talking time but difficultly, that means she was in love and changed her mind now
there are many things to be discussed about this topic
i think boy should not give up!!!