I think they are both responsible and I would take the dog. I don't think either one of them gives a crap about him and she couldn't love him or she wouldn't want someone who will let him starve to death to take him and not take care of him. Do whatever you can get away with safely for yourself and take the dog and find him a home. I would not ordinarily say take someone's dog, but with the situation the way it is, he doesn't deserve that.