I'm jealous you have a job and a girlfriend. sorry, I know this isn't helpful. I see you are struggling.
it sounds like you are a little overtaxed right now and you may want to make a few adjustments in your life so it gets more relaxed? stress isn't so good for depression. at least for me it makes things really worse.
do you have an image in mind what you would your life ideally to be like?
I think your girlfriend should understand if you don't have money left to give to her.
can you calmly explain that you may need a little more time with her or for yourself or whatever is good for you and you would feel more comfortable if there was more money left? -I hope I got this right and that my answer doesn't upset you in any way. just trying to help.