Long story short (plus massively outing) - left my DH a couple of years ago as fell in love with someone else. Nothing physical happened prior to split and had perhaps a month of beginnings of EA (texting, coffee etc) when I realised I had such strong feelings. Split request blindsided XH a little but he acknowledged our relationship difficulties - had a 'make or break' conversation with him where he did nothing to convince me to stay and things would change.
I still now struggle with feeling guilty about how I ended it but I knew at the time deep down there was nothing he could do. I read on here so often that one should end a relationship before embarking on a new one, which I did, plus saw no benefit to XH in spending months 'deciding' when my mind was made up. Was I cruel by ending it like that? Despite therapy and time, I need to make progress quickly on dealing with this as it's a massive weight on my shoulders.
NB. I am now with the 'someone else'. XH and I are amicable and consider him still a close friend.