Fa-ajmilī consists of a linking fāʾ and a feminine singular imperative from Form IV ajmala, yujmilu. In this context it means to handle the matter well, moderately, or graciously.
The structure in ... fa-ajmilī is conditional: the speaker does not welcome separation, but asks that, if it occurs, it should be without harshness. Complaint about coyness stands beside an appeal for fair treatment.
ExpressionFormSense
AzmaʿtiPerfect; feminine addresseeYou have firmly resolved
ṢarmīVerbal noun with suffixSevering ties with me
Fa-ajmilīFeminine imperativeThen act graciously