I would hire a good family law lawyer that is well versed in dealing with mental health issues in custody cases.  There should be lawyer referral services in your area.  You could even contact the family court in getting in touch with resources, like a social worker and a counselor/therapist, both of which could give you excellent advice.  Just because you are bipolar, alone that does not make you an unfit parent.  Without more info, I can't really give anymore advice than that.  But hope it helps a little and good luck.  Hang in there, everything will turn out good in the end-think positive.