Peter Kreeft, in Three Philosophies of Life, writes (p. 106):
There is no physical perpetual motion machine, but there is a spiritual perpetual motion machine: love. Love is perpetually reinforcing: the more we love, the more we are loved, and the more we are loved, the more we love. There is no necessary limit to this process. Even human love is potentially infinite, and divine love is actually infinite. There is no upper limit, not wall, to love … love itself has no tendency to wear down, only to increase.
The multiplicity of love is also found in a memorable cartoon by Bil Keane: