Just how bad a state is my ex wife in? This is what I'm trying to second guess. And then, what the hell do I do about it?

I called round to see a friend of ours, Jo, who put my ex up on one of her recent weekends away from her new partner. It was Jo my ex stayed with the night I told her I didn't want her to move back in here.

"She can stay at ours any time," Jo began to say, "it's only just that we're both working so hard and getting [their son] ready for school in the morning, and it's so tiring, we can't be up in the night."

I started to lose the thread. Surely it can't be that tiring having another adult, albeit a miserable one, staying in your spare bedroom?

"No, she [meaning my ex] was howling in the night, like a dog that's in pain, and I had to get in with her to calm her down."

Shit shit shit.
I felt cold and very sad.

I've seen her do this at least a couple of times, keening with grief, utterly lost to the world around her. Once in the depths of her depression, again when she found out I'd been having an affair. It really does sound like an animal in pain. Frightening. It's like the morning I picked up the phone and heard my Mum telling me my brother was dead.

All I did in the past was tell my ex it'll be alright and that I'll look after her. And in time she calmed down, and in more time, she functioned again. But - clearly - didn't learn how to avoid situations where she is overwhelmed by misery.

I can't do this any more. She's the only one who can make it alright, she's the only one who can look after her. She is going to see a therapist right now. So far, so good. Except for this question, nagging away:

By telling her to sort herself out, by refusing to look after her or take her back, am I condemning her to stay with him when she would have left? And more to the point, am I leaving my son in the middle of that shitty relationship for half his time, week in week out?

My friend Jo has promised to keep a look out. I need to know how bad it gets. I suppose I need to have a plan. What will I do if I think her relationship is becoming bad for our son?