Green’s Dictionary of Slang

(US black) a loved one.

1940		‘Digg Mee’ ‘Observation Post’ in N.Y. Age 9 Nov. 10/4: One day he met his ‘lull’ [...] soon she and he did marry.
1941		‘Digg Mee’ ‘Observation Post’ in N.Y. Age 9 Aug. 9/7: It brings nothing but grief and strife when the lull of your life is another man’s wife.