The truth probably lies somewhere between this admission and the "once a month for three years" accusation. But whatever the case, his confession is classic: "For extended periods of time, I would enjoy victory and rejoice in freedom. Then, from time to time ..." This is the dichotomy of Romans 7, and every mature Christian identifies with it personally and painfully. The teaching I've found most helpful on this subject comes from Unseen Warfare, pp. 83-84:
If you fall into some transgression, quickly turn to the realisation of your weakness and be aware of it. For God allows you to fall for the very purpose of making you more aware of your weakness[.]This method, although very effective, is also not without danger, and God does not always use it, but only when all the other means we have mentioned, which are easier and more natural, fail to lead a man to self-knowledge. Only then does He finally let a man fall into sin, great or small, in accordance with the degree of his pride, conceit and self-reliance. So that where conceit and self-reliance are absent, instructive failures do not occur. Therefore, if you happen to fall, run quickly in your thought to humble self-knowledge and a low opinion and sense of yourself and implore God by persistent prayer to give you true light, so as to realise your nothingness and confirm your heart in disbelief in yourself, lest you again fall into the same or even worse and more destructive sin.
If you fall into some transgression, quickly turn to the realisation of your weakness and be aware of it. For God allows you to fall for the very purpose of making you more aware of your weakness[.]
This method, although very effective, is also not without danger, and God does not always use it, but only when all the other means we have mentioned, which are easier and more natural, fail to lead a man to self-knowledge. Only then does He finally let a man fall into sin, great or small, in accordance with the degree of his pride, conceit and self-reliance. So that where conceit and self-reliance are absent, instructive failures do not occur. Therefore, if you happen to fall, run quickly in your thought to humble self-knowledge and a low opinion and sense of yourself and implore God by persistent prayer to give you true light, so as to realise your nothingness and confirm your heart in disbelief in yourself, lest you again fall into the same or even worse and more destructive sin.