Day late and dollar short.

I guess only you can truly make that call and it will depend on a couple of things.

1.  Can you forgive/move on and still love and respect her.. knowing how she acted in the past?  In other words... are you past the point of no return in your own mind when it comes to her?  or was your decision to leave still possibly a last ditch attempt at a "wake up call" for her?

2.  How genuine do you see her being in these changes.. and to what extent would you want to be involved even if some of these efforts aren't 100% successful when it comes to the skids?

If you feel you still have the ability to love and respect her.. and feel her new leaf is an earnest and full out desire and effort to change things.. then perhaps you have a path forward together.  I would not rush back but suggest counseling for the two of you because I am sure you have plenty to unpack and deal with.  Not saying it will ultimately work out.. but you might be inclined to try.

If you feel that your ability to truly love and respect her has died.. then you owe her the truth.. and THAT is the truth.. that you tried for many years.. and you are sorry but it has to be over.. hopefully you can parent your child in a low conflict way.

I would remain living apart, unless you see REAL evidence that things have changed regarding SS.  

Last weekend you left, and she's seen the light? Nope.

Tell her you are glad to hear it and you look forward to hearing about the progress they make.  You can even still date her, if you want. But don't move back in until you see real change.

I think you need to talk to a lawyer.  Find out what your options are, what impact on potential spousal support another 6 to 12 months of living together will have, whether you need a legal separation with a custody order, etc.  In any event, I agree with those who are saying you should not move back in unless and until you see long term, defiinite changes.  If your wife had any consideration for you, she would have done this BEFORE it got to the point where you felt you needed to leave.  Now it look like a means to an end.  Only she knows exactly what end she's going for and why.   Once she has you back, who knows whether she'll continue, or whether there's any chance of SS changing.  

Recognizing the issue is a great first step but changing years of bad habits can be hard. Give it time to see if she is capable of making the necessary changes. At 15 trying to change the way she parents SS may not be receptive to the changes and this could be a war that you don't want to take part in. 

Take it slow and wait to see proof of changes if you're willing to try to make it work. Only you can decide if it's too late.

Well, that's convenient.

"Don't tell me. Show me."  Only you can answer your question.   Why did it take you calling it quits for her to extricate her head from her butt?

That is the question.   Keeping in mind that the best predictor of future performance is past behavior what are the odds she will stay the course with her own behavior and in holding SS accountable for his behaviors if  you re-engage?

Her "blame(ing)" of SS's behavior on depression has zero element of accountability and ownership.  The smell test on this sets off all kinds of alarms IMHO.

Good luck whatever you choose.

It took me packing a bag and leaving for a few days to get my DH attention years ago.  He promised to change and although it took time and effort, he has continued to work towards being the husband he wants to be to me...not what his adult kids want him to be for them.  I hope her change of heart is sincere since you seem to love her so much.  It is a journey...and encouragement helps a lot.