I know how it is! I wanted to quit so many times!
Early on, I had made a pact with myself... any time I wanted to quit, I gave myself 3 days. If I still wanted to quit three days later, I would. I ended up nursing and pumping until my DD was a week shy of 1 year. And now as I expecting my second child, I have the pump all ready to go!
I found that my pumping frustrations usually stemmed from feeling like I couldn't pump enough milk and from not having time to pump. By waiting a small amount of time for those things to right themselves, I kept myself from making a decision that I would have probably regretted.
Yes, I enjoyed nursing her when we were together, but all in all, I look at my pumping experience as being one of the most self-less things I have ever done.