That's a really complicated question. Every couple is different. Everyone has a different idea of what "love" is. The symptoms that are associated with "love" are just physiological reactions, they are not an accurate measure of someone's "worth" as a romantic partner. That's why some couples "fall in love", but they "fall out of love" when those physiological symptoms wear off around 3 years in, and then they realize that they're not as compatible as they thought.
Love could be considered those physical symptoms, love could be considered the commitment you make to a particular person, love could be considered the feelings that develop after you spend years committed to each other, but the presence of "love symptoms" does not determine the success of a relationship. Compatibility, respect, trust and compassion are the bottom line, if you don't have that, then "love" is just an illusion.