DP’s son moving in

Nope. Keep your own separate houses until DC have properly launched. I wouldn’t want a pot-smoking, mess-making flatmate who pays no rent/bills and has his girlfriend round all the time either, OP!

That's not really the OP's problem. She can simply say that she was so absolutely shocked by his appalling behaviour that she was lost for words. That obviously she has paused the exchange and that a serious conversation needs to happen to see if there is any way of retrieving the situation. That should put the shoe back on the other foot.

This. I would be pulling out, sorry.

The problem that the op has now is that her lack of reaction when he sprung this on her makes it even harder for her to react against it now.
Please gird your loins @maximusss and stand up to him, tell him that you have thought it over and you cannot proceed because he has moved the goal posts.

You have my sympathy. I’d find it really hard and really stressful but it sounds like, like me, you have been through a divorce or breakup and so you know how important it is not to sleepwalk or end up in these situations out of conflict avoidance. I’m terrible at putting this into practice myself and I think he won’t react well but there is just too much at stake.

Phone the solicitors first to put a pause on any paperwork going through for the exchange. It will make you sound serious op, don't let him manipulate you.

I’m sorry but I’d pull out OP. Your DP clearly waited until the last possible moment to tell you to try and ensure you can’t do anything about it. It’s manipulative and duplicitous. I’d pull out and stay in my own home in comfort rather than risk this living arrangement.

You have actually never lived with your DP (staying over, even for extended periods of time is not the same) and he’s expecting you to go from living apart to living with him and his adult son who has challenging behaviours to such an extent his own mother has had enough of him? Absolutely not.

I feel like he's conned you into being able to afford a property for himself and his son. You definitely should have been considered and had a conversation about it. I applaud you for saying it's his son, as many are cold towards step children however, this is also your home that you are contributing towards. Definitely put your foot down NOW, before you are trapped and it becomes a lot harder.

You said ‘Tell the son that of he wants to move in to your house he's responsible for a third of the mortgage payments and bills.’

You need to be careful if linking rent/keep etc. to mortgage costs. Someone ‘paying a third of the mortgage payments and bills’ might contend they have an interest in the house. Rent or keep, by all means but don’t link it to the mortgage costs.

Crappy fathers always try and rope in another woman to do the work they don't want to.

Yup. She's going to buy that house with that shit man. Meanwhile, those of us who have been there and got the shitty tshirt to show for it recognise how her life with him )and his weed-smoking son and his girlfriend on top) will turn out.

What kind of person springs this sort of thing at the eleventh hour before a joint property purchase as if it is a done deal? Not one I would want to tie myself to. But you have to live and learn, I guess.

This man didn't want his son living with him previously. He wants him there when his partner is living with him because he knows that he will be able to make sure that she is the one who bears the brunt of his son's bad behavior.
He wants to be able to score points with his son, get the credit for making his life easier. Score points over his ex because he will now be the favoured parent who lets his son do as he wants.
And all of the cost for this will fall to @maximusss who has been duped, she will be the unpaid maid who cleans up after them.

Not a chance, I'd have a lazy weed smoking slob moving in with me, especially not without a discussion about it.

If his own mother can't put up with him, why should you?

Ok and now she’s had a moment to process it, she’s started this thread saying she knows she’s likely being unreasonable 🤷🏼‍♀️
Doesn’t seem like she feels able to stand up to his manipulation.

Op the son doesn't need to move in, he already has somewhere to live.

Ask yourself why he'd rather move house than start tidying up his mess?

I'd say that part of the reason for her lack of reaction is that he has blindsided her.
It's an ambush, a surprise attack, it leaves you reeling because you can't process it.
The person that you have trusted and have committed yourself to has behaved in a way which is completely at odds with what you believe about them.
You are somewhat in shock, your unconscious takes over, you freeze.

This is a huge red flag.

Is that how your relationship generally works? He does not discuss with you and says what goes and you stay quiet?

Of course not but I'm saying he should be responsible for costs. Unless he thinks he can move in, carry on making a mess and pay fuck all.

And there’s the girlfriend too.
Personally I’d be flatly refusing to proceed, red flags galore OP.

Do not exchange on the new house. You will regret it and be stuck living with a 19 year old you not related to who smokes weed ( he will smoke it indoors if it is cold or wet outside no matter what you say) and has a girlfriend who will be in your house every day. He is also messy.

These are the reasons his mum moans at him.

Stay in your own home.

Some people here are forgetting there's a big difference between want and need. The son doesn't need rehousing because he can't afford his rent or because he needs to be closer to work, he wants to move in so he can have it all his own way, smoke weed, live like a slob and pay nothing for his keep. If his DF lets him move in he's teaching him a very poor lesson for life, don't pay your way, don't try and be reasonable, don't respect others, just do as you like

This is tricky. I think for many of us, our kids will have a home with us as long as we have capacity to offer it. It’s a given. So in that sense I can see your DPs perspective. But to casually mention it is very off. S/he should have discussed it with you. Ideally a long time ago, before this eventuality ever even occurred (what would your feeling be about my DC needing/wanting to move in, this is my feeling on it…). The lack of communication is something that would upset me too.

What a piece of work this man is, he's deliberately waited until she has committed herself and can't pull out of the deal.
And this is his opening move in your shared life together.
I would be telling him that I am no longer on board with this shared purchase.

I don’t think this thread is genuine
No one would allow themselves to be treated like this

I confess I'd wondered myself, though even those often raise discussion points which can be useful to others, but can't agree that no one would let anyone treat them this way

Unfortunately there seem all too many who'll do exactly that

I can’t get over the fact that you didn’t go nuclear when he TOLD you it would be happening!
He is completely unreasonable - please don’t be so passive. This is setting yourself up for a lifetime of giving in to his unreasonable demands.