“True love grows in a mutually happy relationship and not the fulfillment of one party's happiness alone. Love that does not work like that is not real love.”
Related quotes

“Increase of love brings increase of happiness, when it is mutual, and pure as that will be.”
Source: The Tenant of Wildfell Hall (1848), Ch. XLV : Reconciliation; Helen to Gilbert

The Elements of True Piety (c. 1677), The Shorter Leibniz Texts (2006) http://books.google.com/books?id=oFoCY3xJ8nkC&dq edited by Lloyd H. Strickland, p. 189

“There is only one happiness in life, to love and be loved.”

2010s, 2018, A Free People Must Be Virtuous (2018)

Love and Death (1975)