Opio, well said and very well intentioned. However, I think the rest of us are thinking more about the child in this situation. The welfare of the child in the relationship trumps all. IMHO, I would think that that would be enough for the guy to straighten out for his child's sake. Having a woman at his side who stays "for the sake of the child" only enables and emboldens an addicts behavior.
BELIEVE me when I say I know all about addiction and how it affects one's behavior. I also know what it takes to change that behavior to.