I read your letter in the CCLI magazine and felt compelled to respond. I agree that NFP is a difficult path to follow. My husband and I took NFP class last year. I was on birth control pills for many years and began to worry about my health. We had a wonderful teaching couple and began to see the beauty of NFP beyond the health concerns. Despite this NFP has and still is a struggle for us.
My husband travels extensively and is sometimes gone during that crucial Phase III. My cycles have been irregular and leave very little time in Phase I or III for relations. We've had plenty of frustrations. For example, recently we had the opportunity to take two child free trips for the first time in seven years and both happened while we were in Phase II. However, we have not once considered quitting because despite the drawbacks the benefits have been well worth it. I am happier and healthier. The concern about health complications from the pill are gone. Our marriage and faith is stronger. We are doing NFP as a couple where as before I was taking the pill. We talk more and rely on each other to overcome the challenges NFP gives us. My husband understands me as a woman so much more and respects me even more now.
It seems to me by not charting her temperatures regularly your wife is being rather selfish. How can you be certain that her Phase III starts on day 18 each cycle? So much anticipation and excitement of relations is in watching your chart and waiting for the start of Phase III. This increases the spontaneity that you say is missing. I don't like to get up early either but set my alarm for 6:00 am each day, take my temperature and then go back to sleep on the days I can. Most thermometers allow you to take a temperature and read it later.
It seems to me there is more to your problems than NFP. NFP is an easy scapegoat to blame all your problems on but take my word birth control and more sex won't solve your problems. Possibly you and your wife would benefit from counseling for your marriage and taking a refresher course in NFP. Remember we were never promised that following Jesus would be easy. We are asked to take up our cross and follow him.