As a marriage and family therapist, sex therapy is a common part of my practice. Often, people (men) worry that they aren't having as much sex as they used to when they were first married and that must mean there is something wrong with their marriage. This often leads to conflict in the marriage.
The drop-off in frequency is a normal (and believe it or not it's not even bad) change in the normal development of a marriage. However, in our over-sexed (yet under accurately sexually educated) society anything less than lots of mind-blowing sex all the time = "there must be something wrong."
While there's a lot more to this issue, here's one very interesting finding about testosterone in Dads and why the dip in testosterone is not only NOT a bad thing it's actually quite a good thing:Dads Have Less Testosterone I think it's nice to know that men ARE built to also nurture and not just be aggressive. There are many examples of this in other more "primitive" cultures. I believe clearly that many "advanced" cultures have clearly got it wrong where we teach men to be be mostly in tune with aggressive/tough emotions while teaching us to be strangers to our more nurturing/sensitive ones. Both have their place and value. Again, balance vs. extremes.