I think David is trying to say, that a desire for training is not important. Even if you enjoy training, the desire is not necessary. If commitment is based on desire, then what happens when desire is temporarily lost?...well commitment is temporarily lost. Commitment should not be temporary, or it is not true commitment. However, if we want to train it is convenient to us when we have to train, therefore the desire of training is only convenient to need of training. If we understand, that we only have a lifetime to focus on something as large as Aikido, then to even attempt to understand it will take commitment, meaning weather we want to or not, we train. David was saying that Aikido training to a serious practitioner should be like breathing, one does not desire to breath, they simply do. Now I understand anyone could say "I desire to breath" , not true, you desire to live, breathing is innate. Therefore if we simply train, and understand that we train regardless of how we feel that particular day (I.E. "I feel lazy so I'll stay at home", or "I just don't want to"), then in the end it does benefit us. No one "desires" to "screw up" or have a "Bad night", or take a hit, whatever, but all those are part of training, and we accept them as such. Well that's my attempt at understanding David's post. I personally like his post, they make you think
Now, something tells me you are not wanting to give up on Aikido, or you would not of posted here, or still be posting regarding this particular subject. It tells me your looking for a reason either to justify your "Leaving", or reinforce your "Staying", but only you can make this decision. If you do not wish to train in Aikido anymore, then no one will hold it against you, and if you want to continue training, then simply go to class. I understand that the fire may at times feel like it goes out, but it usually comes back. When you do the same techniques 1000 times you tend to get bored, and feel like there is a loss of interest, but repetition is essential to understanding. Basically good Aikido comes from dedication, train whenever possible regardless of "how you feel" and good Aikido will come.
This is all assuming some part of you wishes to return to Aikido, but if that is not the case, then nothing here applies.
Just my opinion, nothing more,