Ahh, annette, that is the free will side of the equation. God gave us free will. It is up to us to choose to love him and follow him.
As far as the abstention during fertile periods go, the Church says something to the effect that there has to be a just reason for avoiding the fertile times, such as spacing your children or maintaining proper stewardship of your finances.
GGB, still learning and struggling with all this too.
