Erich Fromm said this quote
“ Love, experienced thus, is a constant challenge; it is not a resting place, but moving, growing, working together; even when there is harmony or conflict, joy or sadness, is secondary to the fundamental fact that two people experience themselves, rather than by fleeing from themselves. There is only one proof for the presence of love: the depth of the relationship, and the aliveness and strength in each person concerned; this is the fruit by which love is recognized. ”