I wouldn't say you have a problem, necessarily. You're just upset because the senior friends you made aren't at school, so the thought of going back and feeling their absence makes you upset... The thing with your other friends, maybe you feel upset talking to them because they're not your friends that are graduating?
My advice. Spend time with your underclassmen friends, they're still at school. You'll get through this! If the seniors already left, then you shouldn't I've that many days left yourself :) Your friends aren't leaving you forever.. They just won't be at school.
