Getting married to a second or a third is not a valid reason for a Muslim woman to ask for divorce. Other reasons that you mentioned such as not providing you and your child may be valid reasons for divorce. My view is that if you can help him understand his situation and fix his character by making him qualified to take your responsibility and that of your child, you should take all steps to support him and keep this marriage intact for the sole benefit of your child. If you think he will not respond, you can ask for divorce.

 

Allah Almighty knows best.