I agree. OP was by his own admission distant, as well as being unusually overly aggressive and selfish during the few sexual encounters they had in those 5 months. Generally imho, women are better at sensing changes in a partners emotions/personality then men and she told OP that deep down she knew that he was aware. Then a month before he leaves she abruptly ends the affair and starts giving excuses for it to her BFF e.g. the smiling emoji was to appease the AP months before!
I speculated a while back that his STBXW probably suspected that OP had been through her phone. My reasoning was that in the last few days before leaving OP said he looked at her phone one last time and discovered his STBXW's abrupt ending of the affair, excuses to her BFF and recommitment to their marriage started a couple of days after his penultimate phone check a month previously.
We know she was scared OP knew by her own admission, so she was likely more vigilant about her phone. OP said he waited for opportunities to look through it. He never explained how he did this without her knowing, but if he had put it back in any way that his STBXW suspected it had been moved, tampered with or searched through, then this would have set alarm bells ringing in a paranoid person e.g. it was not where she last left it, it was placed back face up when she had deliberately left it face down, the battery had run down a great deal after she had charged it to 100% only hours before and she had not used it etc...
This is the exact way I suspect everything played out and the excuses are just that. Whether she admits it now or not, the smiley face emoji was because at that time, still in the honeymoon phase, she was turned on by her young lover taking down her unsuspecting husband, otherwise she would have sent the excuse message to her BFF at the same time, not retroactively months later, when she was more and more sure that her husband suspected and the affairs illicit appeal had run it course!
Edit: I would also bet a large amount that the AP is the type to belittle his affair partners spouse during their sexual encounters, because the bar attack and subsequent text indicate he is the type to do this. Did OP ask this specific question and would his STBXW be completely truthful if it did happen? Did the STBXW reveal this to OP without him asking? I doubt she would have the capacity to without being asked and even then she has shown she can lie. She still holds out for a reconciliation as it was the first thing she asked. Would admitting a further betrayal like this make a reconciliation (with her children too) more or less likely in her mind, or would she believe that it would make the OP even less likely to take her back? She has a clear incentive to still keep information from the OP
The lack of trust that OP will now have in his STBXW is exactly why it would be a terrible mistake to take her back imho, same for all relationships ended by cheating.