Yes, medical school is a shock for the starters. New science & new culture( completely different from other departments). One has to spend a lot studying even he may not have time to call families/friends. The best you can do is to understand him and never try to reciprocate if you feel like he is ignoring you ( because he is not and he is merely busy and tensed). If he is not calling you as he used to ,call him. If he does not pick the phone its because he is in a library or class. If he is not talking a lot over the phone, it is not because he is changed, its because he is busy. Just be yourself, don't stress him out. May be you are his only source of joy and you are his hiding place from the campus stress, help him have a good time with you when you meet. The good news is this will last maximum of 1 and half years and he will have time for your. The first 1.5-2 years are the most stressful. Things will be good.