Hi again, Thend,
I wonder if maybe you should try confiding in your girlfriend about how much you are hurting on the inside. I understand why you don't want to "wreck it" when things are going well, but you also said that when things are going badly, she doesn't understand the severity of the situation. Honesty and communication are really important in a relationship, and I think you should give her a chance and tell her what is really going on with you.
If you think you are suffering from depression and need some help, I would encourage you to talk to your doctor and see if you can get some counseling. I have been in that dark place myself, Thend, where I was miserable about my life and about myself, and I have found that counseling has really helped me a lot.
As far as letting your loved ones down, and not meeting their expectations, I will say this: I know how important it feels to be who and what everyone wants you to be, but the most important thing is that you find a way to be happy with yourself. Parents and other family members and friends usually want us to be happy more than anything else, and I wonder if maybe you should start talking to your loved ones about how you feel, and why you think you might be letting them down. Again, communication is key.
My heart goes out to you, Thend, and I hate to see you hurting like this. I hope you will consider finding someone professionally to talk to, so that you can find a way to feel better and move forward with your relationships in a healthy way. And welcome to HW...it's a wonderful place to talk to people. I hope you will keep posting.