A person in love is humble. A person who loves has, so to speak, forfeited a part of his narcissism.

Sigmund Freud (1856-1939) Austrian psychoanalyst and neurologist

“On Narcissism: An Introduction [Zur Einführung des Narzißmus],” ch. 3 (1914) [tr. Strachey]
    (Source)

Alternate translations:

The lover is humble. He who loves has, so to speak, forfeited a part of his narcissism.
[tr. Baines/Riviere]

Whoever loves becomes humble. Those who love have, so to speak, pawned a part of their narcissism.
[Source]