To have told NDN that dh won’t be helping her anymore?

She’s either a user or after a replacement baby daddy.

I'd explain that he's not actually helping her in the long run. She needs to learn to be able to manage independently. As PPs have said, it's not easy managing with buggies and babies and stairs, but she needs to work out a method that works for her. She will encounter stairs all over the place in everyday life. At train stations and shops and out walking. She can't have your DH with her all the time, and even if she had a partner she would need to manage on her own day to day. By doing this for her he is actually preventing her developing this independence, so for her sake (as well as yours!) he needs to step back.

If she is suffering from PND or anxiety, she needs to get appropriate support and treatment from her GP/Midwife/Health Visitor.

Do all women think they live with men who can't be trusted not to have sex with anyone they can when they can?
Do you need to keep a eye on them when they go to the toilet in a pub? When they go to work, do their wives think they are secretly going to an orgy?
What a sad world!

I think helpful in terms of occasionally knocking for one off things is being neighbourly. My husband does our elderly neighbour's garden when he is doing ours. I have sorted her bin whenever it's blown over and brought them back in, (until the council started doing it). She knocks in an emergency and we do what we can. She's asked us to be present when someone was trying to sell her something. All those things are fine and agreeable to me, because she is not capable and it's occasional. I would not be happy being interrupted daily while wfh, to do things that I have done myself! There are better coping strategies she could learn and save these knocks for better occaional things like putting together something.

Because his wife is uncomfortable with his developing relationship with this woman! He has overstepped his wife’s boundaries! Not to mention this spiteful madam messaging him behind his wife’s back slagging her off! If life is so hard for the NDN, she can access support from her midwife, GP, health visitor, family and friends. Not overstepping boundaries with her neighbours, who are uncomfortable with this level of contact. Don’t let that get in the way of your narrative though.

Apart from anything else-do people really live in relationships with men who can’t be trusted in the company of another woman? Even if the woman is -and there is no suggestion than the NDN is-a bit flirtatious? Isn’t that exhausting?

Absolutely this

His reaction tells a story, he wasn't sad that his DW didn't want him to help, he was sulky and unpleasant. Helping the NDN out gives his self esteem a boost so he can't see that she's becoming a nuisance. It's one thing to help out now and then but the NDN is looking for help everyday and is becoming dependant on him, that's too far. If she sees him as a Father figure how long before she's asking for babysitting or money.

@CurlewKate It doesn't start out with the man wanting to fuck the neighbour. The man gets a buzz out of helping the helpless young woman. He's the hero. He feels wanted.

The NDN has already tried to make OP look mean. OP's DH sulked about ut.

You deliberately missed @clinellwipe 's point, which was about OP's DH's motivation. Would he be helping the NDN if they weren't young and attractive? Would he be prepared to offer the same amount of daily support to a 75yr old woman - or man? Only OP can know this.

NDN was pushing her luck, and went a bit too far. She should have backed right off, instead she inserted herself into OP's marriage.

She's either very manipulative or very stupid. Time will tell.

The exact opposite- just because she has those attributes he shouldn't be admonished for being helpful.

"Why SHOULD it end"? Because the NDN has totally overstepped all normal social boundaries. Crying to OP's DH because, she claims, OP has been "unkind"? That is not a neighbourly relationship - that is something more.
I have great relationships with all my neighbours - we wave when we see each other from a distance, stop for a quick chat if we bump into each other, occasionally put each others' bins out when one is away on holiday, occasionally take parcels in for each other - exactly what any normal person would expect of a neighbourly relationship. OP's NDN's expectation of a neighbourly relationship is not normal - it's excessive - and I don't believe you would tolerate it if it were happening to you in real life.

What’s your point though? So she’s young and pretty so OP’s DH should be helping her?

EVERYONE likes young attractive people! Hollywood films, daily soaps, adverts, etc. are full of nice-looking people. It's just normal, fgs! Would Eastenders, Emmerdale or Corrie be so popular if the cast all had to be over over the age of 65 years? We can't just banish nice looking people, and our lives would be impoverished if we could.

I agree, she should. I simply answered the OP's question factually because I didn't realise, at the time, that it was rhetorical.

Ah apologies, you weren't the original posted I quoted!

It's strange isn't it? you'd think if he was fine with his own wife doing all that without help he wouldn't feel the need to be on call for this woman 24/7

I don't disagree with you. I was just answering your question which, at the time, I didn't realise was rhetorical.
The NDN needs to become self-sufficient and stop trying to come between OP and her DH.

Definitely something going on between them, not saying they are shagging but something isnt right from your updates.

OP from your morning update, it seems like you really need to sit with DH and talk this over. It sounds like he thinks this has shown you in a poor light and hopefully thats all there is to it. “Banning” him from helping is not going to end well but obviously you have feelings that he should take reasonable account of too.

No, I wouldn't check his phone either OP, but I would be asking him what the matter is - and not letting him get away with fobbing you off.
If he honestly can't see how her crying to him behind your back (trying to come between you), calling you unkind, him defending her to you, instead of defending you to her, and sulking shows that there is something going on, then he's being a disingenuous dick. They may not be having an affair, but there does seem to be some sort of emotional attachment between them which could lead to a physical one. Your DH needs to be reminded of where his responsibilities lie - with you and the children he helped create. In short, he needs to grow the fuck up, remember he's a husband and father, and his family should be his priority.

OP did he worry about you when you were having to do the stairs alone? Checking up on you and being very nurturing? If he wasn't it seems very odd he's so worried about her, when it's something you did yourself for months!

Someone may have said similar so apologies if it’s already been said - but would he be texting and going out of his way to help an older lady (who is still physically able, lets say a healthy 75 year old) with going up and down stairs with bags, driving to appointments. If he would genuinely do that for an elderly woman or a man that is asking for help then he sounds like a truly lovely man (even if a tad annoying!). But I imagine her being a young pretty woman is a HUGE part of this.

So it's perfectly doable then? he wasnt worried about OP doing it for his kids even though she was in exactly the same situation, he just expected her to get on with it using a sling.

So why does that not apply to the neighbour?

There is definitely something going on. I hope someone more knowledgeable than me can advise you what to do next. Don’t doubt your instincts here, if you feel he is pining for her now after what you did, something is definitely going on between them.