My friend is crazy jealous

So we have this friend who has been dating this guy for around three years now but the problem is that she is crazy jealous and he's a man whore. You can tell that she doesn't trust him bc she's always questioning everything that he does. She even has every right to bc he has gotten with one of us and is always telling me that he wants to be with me and everything else. She's caught him doing so many other things though and he always manages to get himself out of it no matter how much we point out to her that he isn't good for And that he is always lying about everything without telling her the direct truth. The only reason I dot say the real truth is bc it has been a long time since that incident and I don't wanna get involved or get myself in trouble. The possibilities are endless with what else he's done since when I got with him was a year ago and she's always fighting with him bc she catches him talking to other girls. She constantly fighting with him over everything says she's done with him and all his bs but two days later gets back with him again. She's basically one of those girls that will do ANYTHING for him and he won't do the same. She acts as if theyre married and were only 18 she has so much ahead of her. What do you guys think about the situation. It's not normal, right?