Thanks to everyone who has responded, so far. The issue of guardianship has come up before...He actually suggested it (long before the relapse), because there are a lot of good, practical reasons to do it. But, I had been a bit resistant to it, at the time. We hadn't been together that long and it seemed like too much too soon. Of course, we hadn't really talked about a *temporary* guardianship, and I was unaware such a thing existed. That might be something to look into.
Probably the biggest obstacle to doing anything legal will be his daughter's mother. She may agree to it, but she might fight it tooth and nail. She still has visitation rights (though she rarely exercises them) and could go to court to fight to get her daughter back...circumstances right now would be perfect, actually.
Zombiewife, the situation with the ex is this. She was, basically, a girl my A had a fling with--no real relationship. She got pregnant. She was already dating someone else by the time she came back and told my A about the pregnancy. He wanted to be a part of the child's life, she sometimes let him see her and sometimes didn't, and there was much battling back-and-forth. He took her to court and, after a couple of years with much evidence the mother couldn't provide proper care (and could even be a danger to her), he won primary custody.
She is bipolar and has had major addiction problems. Last year, she was in a horrible accident. (Her "best friend", who knew she'd copped that day, attacked and beat her for the drugs. After the beating, she left her on a train track--with the full knowledge that the train was due any time. The train did come. She survived, against a lot of odds, but lost a limb.) She is just now coming out of physical rehab and, for the time, is not using anything that's not prescribed. She's about to get her own apartment. This might be the turning point for her to get better, which I hope is the case. This might also be the time she goes right back to her former ways, with all the pain medications she has to take and being back in the "real world" again. Who knows?
I've met her and I have no animosity toward her. I hope she gets well and becomes a part of her daughter's life. I have no desire to stand in the way of that. However, until she's proven she is capable of taking care of her, I would not want her to have the option of gaining full custody because daddy's off on a drug relapse.
Right now, she's trying to get her daughter for the summer...we don't know if this is good or bad or if she has an ulterior motive. She has only seen her daughter once in the last two years, and that was when I took her up to see her in the hospital after the accident. But, if we do allow the summer visit and her dad's problems get worse, that could be a real problem...