Every time I've reached that point that you have described, I've quit. It was the best thing for me every time, too. There is no point wasting your time doing something you don't want to do, especially if it's for someone you care about. You'll just do a shitty job and you don't want to dump shitty jobs on people you care about.
Is it just that the work is boring, or are you being asked to do unethical things? I mean, either way, I would quit, but if it's anything unethical I would urge you to run as fast as possible.
However, if it's just "boring" work, perhaps recasting it in a different light might help. Look at it as a game of seeing how many you can finish in a single week. Stop worrying about doing the "best" job on it. If the project is so boring to you, then you probably shouldn't care so much about the quality of it. Just dump out some garbage, get the checkboxes filled, see how much you can get away with. Make it a learning experience, a chance to test your boundaries.