{When he had spent} (dapan(8873)antos autou). Genitive
absolute. The verb is here used in a bad sense as in  Jas 4:3 .
See on dapan(885c) 烊u 14:28|. {He} (autos). Emphasis. {To be in
want} (hustereisthai). The verb is from husteros, behind or
later (comparative). We use "fall behind" (Vincent) of one in
straitened circumstances. Plummer notes the coincidences of
Providence. The very land was in a famine when the boy had spent
all.