When ENM loses the "E" - processing relationship loss

Hi all - I was a frequent commenter in this sub for the past year or so. 40s M who explored ENM with my then-partner (40s F).

What happened over the course of the past 10ish months is in many ways a tale as old as ENM time, with a crash ending that lost the "E". We started under the shared agreement of "sexual exploration only", she connected with someone, feelings happened, agreements began to be pushed (overnights, travel, etc.). She ultimately revealed, after me asking for pure honesty, that she had fallen in love with this person and was no longer in love with me. The ending on our side was riddled with a series of lies and cover-ups that completely removed the "ethical" element.

In hindsight, I know all the things. I know our relationship wasn't on solid enough ground to open. I know we should have processed things in therapy. I know this new guy is a symptom of a much larger issue.

I never found myself to feel the compersion that is often mentioned among couples who can truly make ENM work. But I know my story may have started as ENM, but over time became plain old dishonesty.

I'm in the early stages of healing. Mostly in the "accepting this is real and happening" stages. What I'd love to know from this group is - has anyone been through something similar / related and found a way through? Whether it was ending the relationship for good, giving it time to evolve into something new, etc. Thanks for reading and for any thoughts you're able to share.