Boundaries, Boundaries, boundaries. It does sound as though the birthmom is dealing with addiction. Might I suggest you look on the Al-non website? There are some good articles about setting boundaries.
http://www.al-anon.alateen.org/
I would ask yourself, "Am I allowing the birthparents to behave in ways I would not tolerate from other family members?" In other words, keep the same standards of safety and personal integrity that you would with other family members. Do you allow someone in your family to keep asking you for assistance? Would you allow a family member to be with your child if they had been using? Making allowances for differences in family culture or grieving is different than making allowances if someone is using. Don't do the latter.
(I hope this makes sense. I have been up half the night with a sunburn.
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