I started Aikido back in '93 and I ran into a problem not all that different from yours. I felt I was going nowhere and I practiced every weekday - sometimes twice a day. It allmost ruined my life. I neglected my studies, I got more and more frustrated not to be a shodan - not to be a Sensei - not to be recommended by my Sensei for my hard work. Finally I quit - not being very happy about myself and feeling quite miserable. I took it up again later for a brief period of time, but ran into the very same problem. Now I have had a three year pause from Aikido and about a month ago I took it up again, and this time I feel so much better about it. I don't really care what color belt I'm wearing or what kyu grade I'm at. I just enjoy training. Sometimes I can't help myself giggeling while doing a Shiohonage where nothing works and if I'm practicing with another beginner they usually look at me very puzzled and sometimes even a bit frightend. I just enjoy exploring the technique and learn a little bit more about myself.
Perhaps what helped me was getting a steady job a wife and a daughter (and turning 30 - that made me think A LOT). These things made me realise how precious time is. I used to feel ashamed if I missed a class but now I am happy taking one class a week and perhaps one extra Iaido-class on a weekday morning. I think I have learned to enjoy what I can get instead of sulking over what I can't get. Sure now and then I can drift away on the 'when I become a black-belt' dream, but it seem less important to me now than ever before.
Ups! this got a little out of hand. Hope it has done any good.