I feel the same way. I honestly don't remember the last time I was genuinely happy. Anyway, I think you should tell your teacher about how you're feeling. If he sees that you're sad, and you feel somewhat comfortable with telling him things, then I think you should confide in him. It would be good to know you have someone to talk to, especially if it's a teacher. Most teachers do care about their students and will help. I'm in high school too and there's a teacher that I talk to about how I feel. I wasn't quite sure if I could really tell my teacher what I'm going through, and I wasn't sure if I would be able to put it in words, but once I talked to my teacher, i was glad that did.