Niall,
As a student of medicine myself, I am going to offer you 2 different forms of advice. Since you are 2nd year, you must forget about this man and move on. If you are a US student, you really need to focus on school and the board exams. I was having a girl problem a while ago which distracted me from my studies too much, and I couldn’t afford it because I’m already getting panic attacks about the boards. I cut her out of my life; she didnt seem to care or maybe is relieved, but who cares about her, once I am done with the step 1 it is easy street after that. Meeting girls or guys can happen anytime and anywhere, but you can only take that exam once. This advice is from a med student perspective.
From my batman perspective, I think that if this man is not over his past girlfriend, that will do more harm to you. You are right, its not fair to you that he is doing this to you. This guy has his own problems it seems, and I would hate to see his problems affect you negatively. You deserve someone who cant stop thinking about you and nobody else. These people do exist, but sometimes you have to branch out of your comfort zone to meet people.
Niall, you do have control over your own life. I need you to answer one simple question, who matters more, yourself or everyone else? If the answer is you, then you need to take care of the most important person in the world, you. I know you feel like you lost yourself sister, I’ve been there, but once you start looking out for yourself, and start focusing on what you are good at, which is your workload, the gears of your life will start moving again, you are the boss Niall.