Those strong attachment bonds can stretch into elderly adulthood as some married couples take their vows of "in sickness and in health" seriously.
A Canadian study of elderly people found many stayed heavily involved in the lives of their spouses who had to go into assisted living facilities.
Some stayed involved by taking classes together, looking through diaries and photo albums, and helping with general caretaking duties.
One 82-year-old man in the study even took weight-training so he could lift his wife in and out of the car for weekly trips home.
This is just one example that true love can be expressed every day, not just on Valentine's Day.
Relationships That Last Forever