Kilānā means “both of us,” referring here to the poet and wolf. Idhā mā nāla shayʾan describes obtaining something; the object pronoun in afātahu points back to that acquired thing.
In man yaḥtarith, man is conditional and yaḥtarith is the jussive imperfect. Ḥarthī wa-ḥarthaka are possessive constructions, literally “my cultivation and yours.” Yahzal gives the consequence, growing lean.
Ḥarth literally belongs to agriculture but is applied here to earning a livelihood and its results. Recognizing the metaphor is essential to understanding the shared struggle to survive attributed to the poet and wolf.