“If you will afflict my daughters, and if you will take wives besides my daughters, no man is with us. See God is witness between me and you.”
Laban deals with his first concern, the security and protection of his daughters. He hands them over to God's protection for their tribe can no longer protect them. God will see whether Jacob treats them rightly. Note especially the provision against Jacob taking other primary wives (concubines would not matter, they are of lower status and would not affect the status of the primary wives).
This can be paralleled to some extent from Nuzi where ‘Nashwi has given his daughter Nuhuya as wife to Wullu. If Wullu takes another wife he forfeits Nashwi's land and buildings.' The parallel is not exact, but it examples restriction being placed on further marriage with a cost involved. Laban clearly does not expect Jacob to marry a further primary wife and would consider it a breach of the covenant, theoretically at least nullifying the promise of non-interference.