I went to wikipedia and saw this...
Originally "honeymoon" simply described the period just after the wedding when things are at their sweetest; it is assumed to wane in a month. The earliest term for this in English was hony moone, which was recorded as early as 1546.
"the idea that the first month of marriage is the sweetest"
In Western culture, the custom of a newlywed couple going on a holiday together originated in early 19th century Great Britain, a concept borrowed from the Indian elite, in the Indian Subcontinent[citation needed]. Upper-class couples would take a "bridal tour", sometimes accompanied by friends or family, to visit relatives who had not been able to attend the wedding. The practice soon spread to the European continent and was known as voyage à la façon anglaise (English-style voyage) in France from the 1820s on.
A honeymoon can also be the first moments a newly-wed couple spend together, or the first holiday they spend together to celebrate their marriage.
"The first month after marriage, when there is nothing but tenderness and pleasure" (Samuel Johnson); originally having no reference to the period of a month, but comparing the mutual affection of newly-married persons to the changing moon which is no sooner full than it begins to wane; now, usually, the holiday spent together by a newly-married couple, before settling down at home."