He cheated and I’m leaving but how do I end it all?

I just found out yesterday that my fiancé of over a year has been cheating on me for the past 3 weeks that he’s been gone to visit his friends and family. I moved across the country with him and we were supposed to live together when he comes back but he forgot to log out of my computer and I saw his history (since he owns a Samsung phone) filled with just him on tinder, looking up how to pick up girls, and probably locations of where he took girls out on dates.

Im breaking up with him right when he comes back but I’m still trying to figure out how to do it cause he’s very manipulative. He’s also an extreme narcissist with anger issues.
3 mo
Update: Im actually leaving before he comes home and I am planning to break up with him through the phone cause I found out from his ex that he threatened to kill himself when she tried to break it off with him. I now just need advice on what to say when I do break it off cause I know I can't be to rash because he still has all my stuff shipping with his things and I need to convince him to give me my things back.
He cheated and I’m leaving but how do I end it all?
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