dean is right, take a break, go on vacation.
don't stop being the nice guy. it is obviously core to who you are, and if you try to change the type of person you are, the worse off you will be. but do start doing more for yourself.
if she can't trust you, be done with her. you can't have a relationship without trust.
as for the depression, i totally understand since i've been through it and am still dealing with it. worst thing to do is to sit around and dwell on it, since it accomplishes nothing. you need to start going out with your friends again. that made you happy before, so start doing it again. forget what your gf thinks. this is about you.