What to do about partners son?

[Anyoldthing]

I was advised to re-post this here for some further advice.

I've been with my guy for 10 months, we don't live together and in that time his 8 year old son has urinated on ceramic decorations at a holiday cottage and climbed out of the windows and thrown stones at the window, encouraged my 5 year olds to cover up, decieve or copy all of the same. Climbed out of a caravan window. Stolen out of my pockets at same caravan. Climbed out of my 5 year old daughters bedroom window and asked them to lie to me.
Following this I sat him down and made him confess what he'd done as my partner wouldn't beleive it (despite confirmation by both of my daughters, footprints on the windowledge, his history of climbing out of windows and his confession) and my partner said I forced him to admit to something he hadn't done. That drives me crazy!
He's also manipulated his father with comments around 'you don't love me' whenever I'm around overnight (especially on holidays), followed by 'I hate you', 'I want to go back to Mummy', 'if you loved me you would......' and pretended to be in serious pain, screamed his head off and cried for hours.
Shoved one of my daughters around. Shoved the other underwater despite knowing she's a none swimmer. Urinated in my garden and lied about it, despite being 10 feet away from a vacant loo then tried to make out my daughter lied.
Run off in woods which left his younger sister with me whilst his Dad went to find him.
Refused to do as he is told or more occasions than I can count.

He freely admits to anyone that his sons behaviour improved when he was taking on board my support and suggestions with his sons behaviour and he admits his son is a pain. He also admits that he often thinks its easier just to give in, because his son will kick, scream, break things and lash out like mad if he doesn't get what he wants. My partner would rather have a somewhat disobedient son that the demon who cant get his own way.

The kids live with their mum, she isn't exactly a good role model but I don't need to detail that here. My partner has them at weekends only and is often not looking forward to it.

My partner and I argue about his son more than anything and I've refused to be around him for the last 3/4 months. During a recent situation his son was banned from cubs and whilst discussing his sons behaviour I suggested that maybe he is being banned for good reason and pointed out that his Dad is very defensive at times and is perhaps overlooking the truth. As usual he went mental and stormed out. Our relationship is teetering on the brink of complete collapse and we're on the very last chance. We had an unexpected pregnancy which resulted in an awful miscarriage just 7 weeks ago and our relationship suffered terribly. He was concerned about what his son would think of the baby more than anything and was unhappy about the pregnancy.

I last saw my partner a week ago, he left in an absolute fury when I pointed out how hurt I was about him saying I bullied his son into confessing. He was also furious that I said maybe the cub leader has a point. Now he says he cannot imagine our relationship can recover from that.

I don't have solutions to our problem and I'm so emotionally overwrought it's hard for me to see through it all. I'd love for us to be a happy blended family but I feel his son comes between us, demonstrates bad behaviour to my kids and manipulates his Dad to our detriment. I love my partner dearly :(

The other information that came out of the previous stuff as questions was:
The parents have been split 18 months.
The ex drinks heavily and has a new partner too. The kids live with her.
The little one is 3 and behaves fairly normally for her age.
My guy feels he cannot control his son and feels my influence massively changed his sons behaviour for the best earlier this year and yet he's offended when I tell him the truth of my opinions.
I know I couldn't reverse this situation and stay in the relationship.
I've worked with the kids to collude on gifts for their Dad, bought them Xmas gifts, gone out, upgraded our holidays to include them all, baked with them, had many days out, had them over to play in the garden and had chats about our situation. I gave up at Easter when it all became too much stress.

Just after that we discovered an accidental pregnancy, my partner was not happy - because he knew his son would react badly. And he was relieved when I miscarried several weeks later. I was devastated at his reaction and the loss.

I want to keep my relationship, I would like for it all to work out although I'm realistic enough to recognise that it won't be plain sailing.
Any advice?

[Anyoldthing]

Oh and my guy and I have known each other 15 years with a great big gap in between. I met his son in October last year.
My kids like him and his kids, though slightly wary of his son. His daughter is little and just likes having more playmates :)

[Petal02]

His reaction to your pregnancy and subsequent miscarriage was awful. This alone should make you head for the hills, leaving him to deal with Hell Boy on his own. You deserve so much better than this.

[SingingTunelessly]

The fact that DP was "relieved" when you miscarried tells you all you need to know. How hard do you want to have to work at this relationship to all the time be second/third/fourth - best anyway? Agree with Petal you deserve much better than this.

[glasscompletelybroken]

If you stick around here long eneough you will see that it's a hard eneough job in the best of circumstances. Given the complete lack of emotional support you had over your misscarriage I can't really understand why you're still there!
As petal said - Run for the hills!

[chelen]

Hi, I'm loathe to just dish out blunt opinion but I agree with the other posters, this sounds like a real uphill battle.

I've found being a SM very tough, even with a super SS and a pretty helpful OH. I think in the circs you describe in your post, it would be awful.