all you can do is concentrate on pulling yourself out of this mess. do the best you can to support yourself and get your act together...don't worry so much about your gf. i'm sure that over time, as you work on yourself, she will notice the changes and appreciate it. you need to get yourself straight first before you can even think about being there for another person. it's a shitty situation, but it's the truth.
i'm a habitual pot smoker too, but i don't let it affect anything else in my life. i work hard and am always looking for better opportunities. i have a second interview coming up for another job at a university in philadelphia. things won't come to you, you need to go out and fight for it. if you are suffering from depression, pot might help you feel slightly better over the course of the day, but it is NOT going to help you get out of the rut you're in. i'm glad you realized that and quit for the time being. that stuff makes you feel awfully good, but it makes you slightly lazy, forgetful, and prevents you from taking things as seriously as you would need to right now. save it for when you are back in a comfortable position and can reward yourself.
when people are in a rut, the hardest part is acknowledging it. people go on doing the same things over and over because they'd rather stay in denial about their problems. you are already past that point. you've acknowledged it, so good for you. now all you need to do is set an action plan. start planning for things in the future. create a spreadsheet and budget your finances...project it all the way out to a year from now, even 2 years from now...that way you'll be able to know for sure that X amount of days from now you will have enough money for a down payment on a car. it'll help motivate you to spend accordingly (think of all the money you'll be saving by not smoking pot!). mark down a date in the future (when you have enough money for your down payment) to withdraw that amount, so it's potentially an expense in the future. then update the spreadsheet every day with all of your expenses, and make sure that you don't go negative at that future date. you've pretty much created a safety for yourself. as long as you don't go negative that day, you'll have enough for your car. getting it set up in the beginning is a big pain in the ass, but i guarantee that it will make your life a hell of a a lot easier and you won't have that stress of "will i have enough or not?" going on in the back of your head all the time...you'll know for sure that you will. pm me if you want me to help you with this...