Erm, don't know how to make you feel better but;
-your ex sounds like a twat so be amused someone else has to put up with not trusting him
-if your ex takes DD out, make the most of your time, you'll feel better if you've done the paperwork
-take DD to the park (how old is she?) at the weekend and chat to other parents or, go somewhere for parents and children (our local church does a social for single parents once a month that my friend felt was great even when she doesn't do religion). I reckon you'll feel better if you talk to other people and make friends-you don't need money to do this, just different things to do
-don't worry about not being able to drink. if you do go out in an evening (if you get the chance) it'll be cheaper and you won't get idiots taking advantage of your drunken stouper.
-don't know what you can do about work but if you're feeling down then it'll be difficult to talk to them rationally and ask for the reasons behind your appraisal and ask what they think you can do to get a better appraisal next time.
-go for a walk at lunchtime if possible, somewhere green. It's normally what makes me sane when I feel I'm losing all positive thought.
Hope you feel better soon.