Military GF

My boyfriend just left for his first deployment to japan.. for 3 years. I’m not going with him and it really upset me, because I must finish school. He just got there and the time zone is so different. Since he left I haven’t felt like myself. I’ve been a bump on a log. He comes home in a year, but it’s not the same. I need advice on how to keep myself from going into a dark hole, and to keep positive because my mind is overthinking everything, and making me question things. I’m also late on my period. Which isn’t a shock since I’m always 60+days late every month.