What is the ruling of Islamic law concerning a husband who marries another woman while neglecting his wife, leaving her in a state of suspension without maintenance or a dowry, and also fails to provide for his child for a year and a half?

A man marrying another wife is permissible if he deals justly between his wives. Abandoning a wife without financial support (nafaqa) or refusing to pay her mahr (dowry) is forbidden, and she has the right to seek divorce if her rights are not fulfilled. Neglecting to financially support a young child is a grave sin, and the wife's right to past maintenance (nafaqa) and what she spent on the child remains a debt owed by the husband. As for "neglecting the guardian," if this means marriage without a guardian, then the marriage is invalid.