Separation anxiety with significant other

Let me stress- my boyfriend and I are very very in love, we have been together for an extensive amount of time and we get along so well, we've never had an argument or even a disagreement of any sort and I love being around him so much, but I get very depressed when he leaves. He's 19 and I'm about to turn 18, he works full time and has an apartment and I still live with my mom, dont drive yet, and have another year of high school left. We see each other about once or twice a week for a couple hours at a time, and when he's with me I just stress about when he'll have to leave and when he finally has to I get so legitimately sad and depressed because he's the only person I ever want to be around. He is my best friend and I am always thinking about him and talking to him, and I was just wondering if this is considered obsessive? If so, how can I keep it under control? I've always been a very clingy person, I just want a little peace of mind! Please help, thank you so much in advance xxxxx