Lost in the blizzard. Me (37f), him (40m) and a huge betrayal, now my world is upside down and I don't know if I can make it

We've lived together 3 years, with plans to marry at the end of this year. There have been many "odd" occurrences involving other women that he deftly and easily explained away. They left me with an uneasy feeling, but I was so in love with him I would choose to believe him. Even though things would sound fishy (I only went out to dinner with her because I was drunk and wanted to keep drinking -- I would have went with anyone!! I'll never do it again, and I'm not going to drink anymore) I would just basically give up and believe him.
​
But now there's no more hiding for me. His affair partner's husband contacted me. This was a huge colossal betrayal because of who she is (long story, but she is someone he swore up and down and sideways that he barely even knew, had never met in real life, etc etc). He carried on this affair right under my nose, acting incredulous when I would be at all suspicious, assuring me repeatedly of his love for me, offering to let me have any access I need to feel comfortable that he's being honest, etc. And yet, all along he was texting her day and night, sending pics of him masturbating to her frequent nudes. He was even texting her on Christmas Day while I prepared dinner for our family. But worst of all, he was telling her he loved her and meeting up with her often for unprotected sex in various hotels near our home. In fact, I have strong suspicion that he had her in my house while I was staying with my sick grandma for the weekend.
​
I found out he gave her a diamond necklace for Christmas -- the same one he gave to me.
​
This affair was very short lived (3 months) and she broke it off because she thought he acted creepy and was a selfish lover (she told me this).
​
I now am fully aware that I've been a total idiot all along and of course he's had multiple affairs I'm absolutely sure of it now. I only happened to find out about this one because her husband literally called me up and texted me horrible screenshots. Him telling her he is in love with her and she's so ****able. My partner at first quickly denied it but upon seeing the pictures turned it around on me (yeah, still not sure about that manoeuvre).
​
Anyway the pain is horrible and intense. My best friend was never really there. He didn't care about me. At all. He's been playing me for a fool all along. I think this was almost a game to him. Throwing out little crumbs about her to totally confuse me and then quickly assuring me he only loves me and doesn't even KNOW her for goodness sakes.
​
Of course I'm leaving. But my head feels hot and blurry. I can't figure out how to leave, so I'm just blindly throwing clothes and items into trash bags and throwing them in my truck. I'm pretty isolated (I worked at home for him in a new city and had only a small circle of friends back home). I'm not crying. I feel dead actually. If anyone has gone through this, please tell me how you survived?
​
tldr: partner not only cheated, he did so with someone he swore I was paranoid about and truly made me believe him. Now nothing in my world makes sense. Does anyone have any advice for getting through this in one piece?


Source.