Mother wants to leave father for another man

I DID NOT MEAN TO SPAM. Glow wouldn't post and when it did it posted multiple times.

My mother told me that she is in love with someone else and that she wants to leave my father for him. My dad is a good guy, he has always taken care of her and us (4 kids). I just couldn't believe it. I feel like I don't even know her anymore because she has always talked about how much she loved my dad. They have been together almost 26 years. They met when they were teenagers. I'm the only person she told and I hate that she told me because I dont know what to do. She was expecting me to support her but I couldn't. I can't support her leaving my father for some stranger. Who she apparently hasn't even talked to in a long time. She said she's loved him for awhile because of the way he looks at her and the way he talks to her and apparently my dad doesnt do that with her. Honestly, I feel betrayed. I told her that she shouldn't leave for this man because it'll tear our family apart. It would put my father into a depression and he'd eventually end up killing himself one way or another. My youngest sibling is only 10 and im worried how it would affect her. I am so mad. I feel like i resent her for even thinking of leaving for this man she doesn't even talk to and his 2 kids. I would never consider him my father and I would probably stop talking to my mother. Their anniversary is coming up and my dad was making plans to do something special for my mom and she does this. She told me she would let it go when I told her it'd ruin everything and now i know she's moping and hurt thinking she'll never be happy. She is lonely and trying to find someone to pay attention to her. I've been crying nonstop. I don't know what to do. Am I being too harsh or is my mom in the wrong for doing this to us?

Edit:

Yikes you obviously have some unsolved issues and rage 😂 just because i put that i didnt spam on purpose as a response to your other comment. Chill out lady. And I never TOLD her I was cutting her out. I said I was feeling that way. Im a kid who still lives at home with my parents in a tiny apartment where there is no abuse going on. Also, he never said he'd kill himself if she left. I AM saying he would do it when she leaves because it would hurt him. Why are you acting like I'm responsible for fixing their problems? Reported.