I just want to thank everyone again for their comments. I was in a very low place when I wrote this and I seem to be coming out of it. I could write pages and pages of philosophical crap about how, really, there is no such thing as "the self" and that what I think of as "myself" is really a complex of relations with other things, but I'll spare you.
Two things that I know I have to work on are boundaries and acceptance of limitations - to set limits for myself to define myself and to accept that I can't control everything. Easier said than done, but the past couple days I've had more success by consciously trying to do this.