Give the relationship about four years, we are programmed like foxes.

Evolutionary psychologists have recently turned their sights
on love and divorce. It didn't take long for them
to determine that when people fall in love, there is a period
of up to three/four years during which the infatuation rides at
a peak. The body and brain are whizzing along on a 'love'
drug. Then it begins to decline. From this evolutionary psychologists
perspective we are preprogrammed to lose interest in a
sexual partner approximatly the time it takes to
raise a child  which is on average three to four years.
In this sense we are not unlike foxes where a pair will bond
for a breeding season, stick around just long enough to raise
the offspring, and then vamoose. Canny critters.