What do you do when he stops putting in effort?

I've always prided myself on having the highest of standards -- I've been on lots of dates but always removed myself from the situation before I got too involved if something didn't sit right with me.

I met someone last year and we hit it off. It was very slow at first, he took me out to nice dates, paid for everything, and was just very consistent with his communication. He asked me to be exclusive and his girlfriend about a month and half in, and when we were LD for a while, he called almost every single day. I've met his dad, he introduced me to his friends, yada yada yada.

When he got back I noticed that his communication was off. We're both doing very demanding degrees and it's exam season now, so stakes are high. He still took me out on nice dates, we had lunch every other day together, and he even did a big surprise for me before he left. He's been away for a while now, and his communication is dwindling. He called me the first three days, but I noticed that if I don't initiate the conversation, he won't text me at all. Now, deep in my heart, I know the answer to this -- if someone can go a day without talking to you, they can go a lifetime without talking to you. I'm unsure how to approach this and I'm feeling confused and upset.

I've always keep my heart on the backshelf and that's what I precisely did when he was courting me, but I've realized that I fell and got attached now. My exams are coming up and I want to deal with this without a) screwing up my grades, and b) minimizing the trauma and pain.