What is the interpretation of these fluctuating emotions towards a classmate, are they symptoms of obsessive-compulsive disorder, and how can one get rid of them?

It is not permissible to supplicate against a young man unjustly. The limits of Islamic law must be observed when dealing with non-mahram men, and one must avoid causes of temptation and suspicious situations. One must also lower the gaze and maintain modesty and proper Islamic dress. This is out of regard for the right of Allah and an adherence to His boundaries.