Talk about where to go from there. First time it happened, he just left.
Second husband, I was expecting it. We decided to get a divorce but lived together until our lease was up. I took that time find to find where I wanted to be.
I'm different than most because once I found out all affection was gone and I was basically indifferent to anything that included them.
If he is living with you, toss his stuff onto the lawn and change the locks.
If you are living with him (WHY?) then get your stuff and move out, delete him from all social media, and if anyone asks about him just casually remark that "Things didn't work out," and change the subject.
When my ex husband cheated on me I did this, but when asked why, I'd say, "He wasn't into monogamy."
Start dating again, immediately. Never complain about your ex to your new dating prospects, or act clingy or needy, just go on about your life like it never happened. You can cry with your girlfriends in private.
I drop kicked a refrigerator and dented it. I was a teensy bit upset. Of course, it was 2 weeks before the wedding and he was with someone who claimed I was her BFF. (Before you ask, no wedding happened.)
Pack my shit & leave. We're poly. If he's cheating, thst means he lied, had to sneak around hiding things & stole time &lied to cover that up. All he had to do is say, "hey, gonna pursue a relationship w/ X." My response, "great. Don't forget to use condoms."
Congratulations...you are the first one I have encountered that understands, the real cheat, the authentic cheat, IS THE LIE....