I'd follow thru on what you stated, "I said multiple times, if he comes back then I will have to leave."  Leave, find your own more permanent place.  You don't have to necessarily divorce, at least not right away.

You may not know this, but your wife made her choice long ago.  It is easy in these situations to blame the SK, but my guess is your wife let her son run wild, and with little discipline for years.  Rather than treating her son like a son and you like a husband, my guess is she convulted or mixed up both of these roles, such as complaining to him about you or not correcting him when he made fun of us.  This made it appear to her son that he was THE man in charge.

So, to you it may feel like you are suddenly faced with a huge dilemma, but, again, you were set up for this long ago.  If parents don't parent and allow their children to run feral and don't guide and correct their behavior, then the kids are going to think they can do whatever they want and treat whomever they want as bad as they want.  AND, if SS did abuse you, as you say, you should have called the police.  No question about it.  Neither of you called him out on his behavior as you should have, although that certainly should have been largely done by his mom.

So, leave.  Take your  money and important belongings with you to your new flat.  Let your wife and her son duke it out, if you want to put it that way--hopefully only figuratively and not literally.  See where the chips fall over the next few months.  If they seem happy, and they may be happy, living more like husband and wife, then you have your answer.  Divorce and do your best to move on.  Because your wife allowed this, your SS will never have any respect for you.  Don't fool yourself.  Since you've been putting up with this for years already, I'd say one day is too long, much less six months; and, I have a feeling, next thing you know, it'll be another six months and then another.  Best of luck to you!  This does truly suck.

ETA:  Ha!  Your wife has been putting her marriage at risk for years.  I'd tell her she's way too late on that angle--"Oh, pls.  Just hang around another couple of months!  I'd never do anything to put our marriage at risk."  She's way, way too late on that, and she is not so innocent as she tries to make herself out to be.

Personally, I would never move back in because of how your wife has behaved right down the line, with her son.  She has colluded with his abuse of you, and this will never change.  Find someone who appreciates you enough to value you and not subject you to this kind of crap from another adult.  She is enabling her abusive son, and will continue to do so.  Do you want to be a part of this? 

She is a write off.   She made her choice.  Let her live that crappy decision.

Good for you for moving out. I agree about the nanny cams. 

This almost adult hasn’t really had any consequences for his behaviour and is likely not to change any time soon. 

If this were my son I would make them go to a psychiatrist as a term and condition of living in my home, with also an anger management course, and possibly cognitive behavioural therapy eventually (one step at a time or he would be overwhelmed) which would teach him we are all responsible for our own behaviour. 

If you want to give this one last go, you have been together a long time so I can see why you would. 

I agree with some other people in respect that if he moves out, then moves in again - You might want to find somewhere more permanent. 

The parent stuck in pity mode for their son isn’t doing anybody any favours. All it appears to be doing is making themselves temporarily feel less ‘guilty’. 

Dude, seriously! I can't believe you are allowing this to happen. Grab your balls and do what needs to be done. You have it in you. You know this situation is ridiculous. Get in that house, call the police and kick him out. Take what is yours. 

Time for a blanket party for that POS molesting violent teen. That violent bastard would never risk sleep if he was in my home.  Size can be overcome by blunt objects and never forget that experience and treachery will overcome youth and inexperience every time.

Keep loading his police record with his shit and eliminate your toxic bride's opportunity to take your daughters when she moves out with her polluted womb wombat.  

Get  your daughters and keep them away from the shallow and polluted half of their gene pool.  This woman has no business in your fie or the life of young daughters.  Though she may be their BM.

Don't let your crappy choice of a spawning partner ruin your life or the lives of  your daughters. 

smh

her loyalties are, and they are not with you. This is a sick merry-go-round you will never get off of if you keep going back to her. She is allowing him to badmouth you and abuse you. YOU SLEPT IN YOUR CAR OUT OF FEAR!!! Let that reverberate into your brain waves. Let it get down into those deep crevices and folds inside your head. This woman is a terrible wife if she would even consider allowing him back in the home. She not only considered it, but DID IT, KNOWING YOU ARE AFRAID OF HER MONSTER.

Please get help and try to move on and salvage what life you have left ahead of you. You will not change what you refuse to confront, and nothing will change until you're sick and tired of being sick and tired.

Best regards.