How to tell my friend I think she should leave her bf

He’s not a good guy and doesn’t show her affection and even said once that he would hook up with a girl while he was drunk. He doesn’t treat her right and it makes her really sad. It’s so toxic and I don’t want her to think this is how it should be. She should be happy with him. I don’t want to get into all the details but I promise I know this is something she should do. I’ve talked to many people about it to make sure they agree. How do I tell her?