While I cannot say that I have experienced a "true", once in a lifetime love, I do believe that I know what love is.
Love, to me, is not just an emotion, but also a thing or a person or a memory or a place.  

Love can be a memory or moment.
Love can be the blissful lazy Sundays spent with your favorite people after a long night.
Love can be the family meal with sudden, abrupt laughter that just bubbles up from your throat.
Love can be the hugs you never knew you needed and the words you thought you'd never hear.
Love can be that favorite song that makes you want to scream its lyrics until your voice is hoarse.

Love can be a thing.
Love can be the last gift your grandmother gave you.
Love can be a picture of your best friend right after you did the flamingo challenge.
Love can be a book of poems that gave you the start you desperately wanted.

Love can be any place.
Love can be a library that gives you an endless amount of worlds to choose from.
Love can be the school cafeteria where you spend your favorite minutes of every day with the people who make you laugh and not care about how you may be perceived by others.
Love can be the small space in the back of the house where you paint and listen to the rain.

Love can be anything or everything or both.
It can be life, and it can be warmth, and it can be the good standing hand in hand with the bad, and it can be what makes you happiest.

I do not believe that you have to have a significant other to have love, I believe that you can be fulfilled by others and by the things you enjoy.

Love is just, love.