I don't think there are hard and fast "rules" about what is "ok" and what is not. Do you think what happened isn't ok because YOU think that or because somewhere along the way you were taught that was the "rule" and the "way things are"?
I have a friend who is married and has been separated (not even legally just separated) from her husband for I don't know 8 years now. He has a live in girlfriend and she of course is dating....do some people disapprove? Yes...so what? All that matters is how THEY (the people involved not the peanut gallery) feel about it.
And...I personally don't think a piece of paper means squat if the marriage has no emotional or physical basis....that's just me. I don't know about your marriage but in mine it was non-physical and non-emotional for YEARS before I left...I may have been living there existing but I certainly wasn't married in the true sense of the word. All that said one thing I do know about the couple I mentioned above as well as me and my XRAH (legally separated only) - we are honest about what is happening....
Slippery slope...I don't know...does it matter? Does talking to someone make you a bad person...not in my eyes....in the end you know you situation and you know in your gut what you want....what a bunch of people say matters not...it's just a matter of finding that gut and following it IMHO.
(I have no idea what the point of my post is...eessh...but I'll leave it in case there is something in there)
PS - I had those insecurities about not being able to find someone once I left....I am dating a younger guy and have others I've dated here and there...there is no shortage (and no I'm not dating to "distract" myself - how ridiculous - I'm dating because I'm FINALLY living after years of not doing so in an alcoholic marriage)