I was dating a man for almost 1 year. We married 6 months ago. My husband has full custody of his 18 month old son. My husband is a recovering addict and lost his job recently. He walked out of the house last week and hasn't been back. He left without his son and said someday he will come back for him. Do I have any legal rights to keep his son??

No, if the boy's mother shows up to claim him, she can. You currently have no legal claim to the child.

You have no right at all, if this is not a temp issue, the mother can come and get the child anytime, and use this to take custody away from him.

I do have to ask, how did a drug addict get custody of his son