Mawlā can describe several relationships in Arabic: helper, protector, ally, or someone bound through a close association. Here the poet speaks of a relative from whom he expects support. Restricting the term to the technical sense “manumitter” would misread this context.
The recurrence fa-law kāna mawlāya ... wa-lākinna mawlāya puts the protector he wishes he had opposite the protector he actually has. This contrast prepares for the exceptionally forceful description of emotional pressure in the next verse.