How do i respond to my friend with her bad relationship?

[Hoursandminutes]

Hi ladies I really need your help!

How can I react/what do i say to my friend who is in a really rubbish situation with her partner?
She always moans, makes comments and seems genuinely depressed about her relationship.
Her bf is very immature, he never makes any effort and won't give her commitment. He says he wants marriage and kids but won't make the step. She's given him ultimatums but that never works! He has cheated before (not on my friend) but I think he's bad news. There are loads of other things which are massive red flags.

What or how do i respond when she is moaning/upset about him and their relationship? how can i be a good friend? I have tried every angle ...sympathy, empathy, asked some tricky questions she probably doesn't want to consider.

I now have to psych myself up when I see her because it's like walking on eggshells!

@Hoursandminutes people like this can't cope without drama or being alone. I think often their self worth is defined by this. My friend is exactly this but as I keep saying, it's their path to follow despite everyone else thinking it's a car crash waiting to happen! I still love my friend dearly even though her choices aren't the same as I would make. But whatever makes her happy, as long as it's not hurting anyone.