Turtle, I dunno. Both kids of mine 13 and16 know that their Dad was one who left. I said basically that he wasn't unhappy with the marriage to me and when someone you love is unhappy sometimes you just gotta let them do what they need to do to find some balance again.
That being said, up until a month or so ago, D thought it was my fault, that I had asked H to leave. Son has known Dad has GF for sometime, but to put it in S16 words " has his head up his ass..." Lol
So, my point is they make their own observations and judgements based on what they see, I think, and what they hear is mitigated by actions and observations of interactions between the parents and all of you as a family ..