Hi, it sounds like you're under a fair bit of pressure at the minute with everything, schoolwork etc. For the schoolwork/assignments do you think you could talk to a teacher/tutor about some of the difficulties you're having? I'm guessing you're falling into a bit of a cycle of depression, not feeling like completing stuff or not doing as well, falling behind, feeling bad about it all (in fact everything)...............Perhaps if you had either a bit of breathing space or some techniques in helping you complete assignments/schoolwork that might help just a little??
As for you're not up to everyone else around you though........everyone has their weaknesses however good you think those around you are at something there are going to be plenty of people who are better than them at other things, and if you look inside yourself I'm sure there will be things YOU'RE better at than them. Now that can be in anything and often the smaller things matter just as much, if not more, than the bigger things.
And let's face it how well do you think that some of them would do, coping with some of the things you've gone through/are going through?? It's my guess that plenty of those wouldn't manage half as well (and that's not meant to be taking anything away from how you're feeling).
And of course you know with depression you can often focus a lot more on what you aren't/can't do than what you ARE/CAN DO and see big negatives when in actuality things aren't really quite so significant. Plus maybe you're not noticing others mistakes quite as much e.g. in rehearsal if you're focusing a little too much on you think you could do better????
Have you talked about this with your therapist as well? Maybe it would help if you haven't?

But last thing (!!) I've got to say (!!) Do you think you should get your tendon checked out medically in case you need any treatment for it (that's if you haven't already)?

Here if you want to talk more though............

Alison