Hi FMY,
" the meeting seemed to go well". So what happens after the week is up? Is he moving back with you? In with another friend? Like others on this board have expressed..(especially in light of the new law suit) you need to cover your back. I don't know what state you're from, but they all require parental responsibility for minors. If you have been assigned custody, or primary custody, you are responsible for him. That includes providing the basics of food, shelter and education. If you have decided to legally abdicate your parental rights of him; that's another story. I assume that your ex is trying to get out of paying child support and that is the reason behind his suit/custody battle. I would not trust that this other family (didn't you say they were friends with your ex?) is not trying to build a supporting case against your lack of parental responsibilities. Honestly, what do you know about their criminal, emotional or moral backgrounds? The fact that they did not discuss having your son show up and stay at their house is a BIG red flag to me. I guess I don't understand what the end goal is here. You seem happy with him living elsewhere (I get that..we've all wished our teens were someone else's problem at one time or another), but not with his father because of the abuse. Do you want him home with you? In a treatment facility? Group home?
I think you need to create a timeline of the incidents and what you have done in response to them. Get child services involved. Speak to an attorney. An objective third party, like a judge, may look at your actions as abandonment or neglect. (I'm not saying they were) If he will not be returning home, you need to make this legal. He may be placed in a halfway house or group home until he turns 18. You do not want to risk losing your daughter because of the way this situation may be perceived. Once it is in the hands of a judge or arbitrator, anything is possible.
Good luck...I hope it works out for everyone.