To really not understand why some people stay in relationships full of arguments and unhappiness. If you do, why?!

Not even unhappy relationships full of arguments, I can’t imagine staying in a relationship where we were just housemates and not partners in any romantic/sexual sense, but there seem to be plenty of them about.

DH and I had rough years and this was one big reason to stay. We couldn't afford separate lives unless we'd had 2 small flats for 3 children to move between. That, and the constant hope it would improve. It did, on and off but more off. Now the kids are teenagers we are much better. I regret many things about my behaviour, and I'm aware it was really bad modelling for my DC, but I don't regret staying together. I also think the one good thing is it taught them not to run away as soon as a relationship goes through difficult times. Hopefully they will sort things out quicker than DH or I did though.

Some are co-dependent. The couldn't, or think they couldn't, survive without the other person.
I think sometimes it's also the only way they know how to relate to people so if they left, they'd probably find a relationship with similar dynamics.
I was raised in such an environment. It's horrendous. Worst of all they congratulate themselves on staying together because coming from a broken home damages the children

I think it’s probably one of them can’t cope with the demands of everyday life (work, kid, house etc..) and takes it out on the other. Then it escalates. Doesn’t mean they don’t love it each other. Probably just need a trip to the doctor for some pills.

'Loving the drama' is an awful thing to say, akin to 'she asked for it'

Sometimes it’s better the devil you know. Sometimes a chaotic childhood or witnessing the same dynamics in your parents relationship sets the standard for your own relationships.

There is a cost of living crisis, people are barely making ends meet with two incomes. Women are often the lower earners or stay at home mums, how are they supposed to buy a house and manage all of the bills? Rentals are extortionate if you can even get one.

I left before the COL crisis hit, it if I had to made the same decision today I don’t think I could afford to leave.

I was pondering this last night. A couple in their late 50s walked past my house last night arguing. "I don't know why you bother coming out on walks you always make it a fucking argument" she was yelling and he was yelling back "I'm not arguing you're the one that's arguing you stupid fucking cow"... and I was a bit WTF? Their whole body language, the way he walked about 10 steps in front of her - they clearly don't like each other much, tone was awful. Life is too short for that.

Surely you understand everyone is individual and although you couldn't or wouldn't put up with it not everyone will feel/think/behave like you...

You could imagine it if your income alone wouldn't pay all bills, rent/mortgage, car/travel, etc surely?

I'm willing to guess that your friend cant support herself and her son without her partners money? So there's your answer.

Another pp said about loving the drama. My mum certainly did - a victim of domestic abuse who absolutely loved all the attention and support she got.

No idea.
Not me but my parents.
The consequences for children bought up in that environment is fucking horrendous.
I was perpetually embarrassed, ashamed and on edge.
They did it anywhere, didn’t care who heard or that we kids were in the midst of it day and night. It was constant.
They hated each other and we were neglected because they were too busy hating each other.
Constantly angry which meant we got the brunt of it.
They were never not angry.
Madness that they stuck it out for 20 odd years.

The stigma there seems to be for some people about being single. Feeling somehow not being in a relationship is a form of failure.

I stayed out of fear I’d be alone and because I feared the time I’d already wasted on the relationship. I left and relished being alone now my standards are sky high and DH (who had similar wasted years) and I both know our worth and strive everyday to be the best husband and wife we can be.

Yeah I'd say money too.

Also, sometimes it's what you are comfortable with because you were raised that way so think it's normal.

Money. Lifestyle. Loving the drama. Low expectations. Poor self esteem. Fear of change.