It sounds to me like leaving this job could be a good move. That said, I am a little worried by the tone of your post. You say that you "think" you are quitting your job today and that you've been borderline depressed. I don't think it is wise to go in and quit your job on a day when you are uncertain and still haven't made a final decision. Posting on this forum was a good move, and you've gotten a lot of high quality encouragement from other commenters which could help you make a decision. If you decide to quit your job, then go ahead, make that decision, and then sit on it for a few days. I doubt that it makes a big difference whether you quit your job today or next week. Once you're sure that you're not making a rash decision in the heat of the moment, go ahead and quit. You can use the time between now and the time you quit to plan your exit. I recommend giving a couple of weeks notice that you're leaving and winding down your job in an orderly fashion without burning bridges.
Sorry, to clarify, the "think" part of the headline was actually due to the contingency that this friend send me the contract in time for me to read it, approve, and quit before the end of the day. It had nothing to do with uncertainty.
