Translation:I left my wife because she was with another man.
Scar mé ó mo bhean chéile ... would be better in this circumstance.
"D'fhág mé mo bhean chéile is fine; the rest is just a word for word English statement which you understand because you speak English. I don't like "mar" used as a catchall for "because" but that may just be what I am used to. chuaigh sí le fear eile would express exactly why the husband is so upset.
So your rather sweeping condemnation comes down to the use of "bhí" rather than "chuaigh"?
What about "d'imigh sí le fear eile"?
The thing is, though, that they are all idioms that require cultural knowledge to understand that "went with"/"chuaigh le" means more than it says on the surface, and the cultural knowledge of contemporary Irish speakers includes "be with" in that particular sense.
I think the question here isn't whether the cultural knowledge of a contemporary Irish speaker would include this, but whether a contemporary native Irish speaker would produce the sentence in question. I wouldn't be surprised either way, but it struck me that this sentence could well just be Béarlachas.
Did you deliberately switch between "contemporary Irish speaker" and "contemporary native Irish speakers"?
By the time any native Irish speaker is old enough to be discussing marital infidelity, they have been completely immersed in the English language for most of their lives, and, as with most young people growing up today, they are far more likely to be exposed to the concept in TV and movies (in English) than at the family dinner table in Irish.
That's the stark reality of the Irish language today - Peig might have used different words to describe the same thing, but if "mo bhadhsaicil" isn't considered béarlachas (after all, it's only used by native speakers - everyone else learns to say "mo rothar"), then can you dismiss a usage that contemporary native speakers use, even if that usage is informed by their knowledge of the equivalent idiom in English?
It might be useful to point out that this isn't just an idiom, it's a euphemism, and euphemisms are often different between generations.
So how would you say this in Irish
Scar mé ó mo bhean chéile toisc gur luigh sí le fear eile ?
Scar mé ó mo bhean chéile toisc nár fhan sí dílis dom ?