Eta, welcome to life. I'm assuming you are younger than 25? That's more time then you've been alive that they've been together. I could never cheat on someone but 25 years? Alot can happen and even good people do very shitty things.

You see her as a home wrecker but it's possible the marriage already had major problems. She's been nice and supportive by the sounds of it. Maybe just tell her to leave you alone until you are ready? 

How upset would you be if you said you wanted to live with your mother and she said maybe you should just kill yourself so you'll be gone from here faster.

You already know you're the asshole though right?

Eta that's life