I agree with turquoisesea. It's not this girl's job to make you happy. I have struggled with depression, and it is difficult for those close to me when I'm down, but I always stress to them that all I need is to know someone is there for me, and it's not their job to make me happy. It upsets them when I'm down because they care, but they also know that I have an illness that makes it impossible for me to "snap out of it" or "cheer up" and sometimes all I need is to know that they care. Maybe if you told this girl that she doesn't have to make you happy, just support you when you're feeling down, things might be a little easier with her.

Also, have you thought about telling a professional like a school counsellor about all your problems? It can feel good to get it out, especially to someone who is neutral and whose job it is to listen and give advice to help you figure out what's going to work for and is good for you. Plus it's completely confidential, and I always liked the idea of letting everything out in the counsellor's office, and knowing that it'll stay there.

Sending you lots of hugs.