How do I give him more space?

Ive been with my boyfriend for 8 years now. I go to medical out of country (3 hour time difference) and he lives in California. He has came and stayed with me for 1.5months so he could prepare for the Medical Exam himself. He left, about 2 weeks ago and after I have been really missing him. He completed his exam, so now he is hanging out with his friends and taking care of his sister, which leaves little to no time to to talk to me. I understand he is finally stress free but he seems to ignore me sometimes and make it seem like he doesn't miss me. I get upset at him basically every other night because of it. i guess I need to give him some space, but how can I do that when I feel unloved? I mean we are in a long distance relationship and I am in medical school, I feel like he should make sometime out of the day to call me and ask how i am doing!