Is my daughter's maternal uncle through rada'a (nursing) unlawful for me (to marry)?

This young man is not a mahram to you by virtue of being your foster daughter's maternal uncle, for he is a stranger to you. If the husband suspects his wife of trying to attract this man's attention, then this is ill-confounded suspicion, unless there is actual cause for concern. In such a case, the husband is not to be blamed for his fear concerning his wife and his eagerness for her to avoid strange men, as this is a praiseworthy form of jealousy (gheerah). The woman proves her innocence through her upright conduct, good character, her commitment to modesty and hijab, her adherence to Islamic regulations in dealing with strangers, and her avoidance of suspicious situations.