How to end a toxic relationship?

My brother has a girlfriend for some time now. Unfortunately, I would describe this relationship as a toxic relationship and it's not just me who thinks so, but my whole family. She's one of the typical gold diggers. She wants to make a comfortable and easy life for herself at the expense of others. Somehow the love is only one-sided. She behaves more like a princess - she expects, but gives nothing in return. I think you should always support each other in a relationship. And currently he's under sooo much stress at work.
Unfortunately, I just don't know how to approach him about it. He reacts very dismissively to the slightest criticism.

Do you have any tips for me?
My brother is very important to me and I don't want him to regret this at some point.

Thank you for your answers.
How to end a toxic relationship?
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