I'm still going through the motions of 'Did I do the right thing?' I feel terrible, almost like I failed...failed her in particular.
The only way you can fail someone in a relationship, IMO, is to lie to them (or yourself) and waste their time staying with when it's not working / keeping that bit secret. That takes away their choices (to stay and try and see if it can work if XYZ is changed, or can be changed... Or to go... The mutual decision thing), and their chances to find someone who can be a partner to them & they can be a partner in return. Cheating is only one example of that kind of betrayal, although it's one of the better known ones. Doesn't mean it's wrong to stay together when things are hard, or you don't
know if it will work, or not. But if you know this isn't going to work for you? You don't string them along, lie, and betray them. You find your balls, and do the right thing, and break up with them. Just because a relationship fails, doesn't mean the individuals in the relationship failed.
...it is easier for them to believe you're just a liar, cheat etc because then you're so much easier to hate, this is why they argue with or ignore the contrary evidence.
This alone would have been more than enough for me to end it, with whomever, & whatever their issues are/were. Anyone who hates me? Can kiss my ass. Sayonara.
But that's the thing about dating, though. It's all about lining up preferences. And everyone's preferences and personal scales of what they love-like-don't mind-dislike-cannot abide? Are different. You put up with a helluva lot of bullshit I don't tolerate at all, meanwhile I have no problem with the thing that ended you two. Everyone has their own spectrums.
You're bad, they're safer without you etc. Projecting that onto you would reduce the guilt of cutting you out.
I'm the opposite. I'm a terrible person & I know it, they're safer without me. The guilt comes with staying, not leaving.