From the viewpoint of a BW, the trouble with TT or lying is that, no matter how loving the gesture or how true the sentiment was at the time that you gave it to your BS, when the lie or the TT is exposed, it's as if it was never said. Actually, in many ways, it's worse than if you never made that gesture in the first place. Because the lie, the TT, puts everything into doubt. It makes the BS think that Everything was a lie. There was no truth. It puts doubt onto every memory.
Let me give you an example from my own situation.
After a bit over a year of being an ideal, remorseful spouse, one day I found that my FWH had lied to me about such a basic agreed-upon demand, that I consider it my DDay #2. For over a year, he held me when I triggered, put a tracker on his phone, called me when he was going to be late, did IC, did MC (which we "graduated" from), and did everything that you would expect someone who truly loved you, owned his decisions, would do. At the time, we were 2/3 of the way through a marriage-enrichment program. And during the entire time, with me asking if there was anything else, was he hiding anything from me, he lied to my face, blatantly, intentionally, and as he admitted, knowing that this lie, if/when it came out, would hurt me immensely.
When it did, I left him. I walked out the door to a hotel while he was gone from the house packed up my bags and left. Because I could not figure out why someone who had shown me such love, could continue to lie to me. That the entire year must have been a lie. That I had bought the pretty picture, hook, line, and sinker, and I was a fool because everything I had done to try to heal, was wasted because it was all a lie. All of my trust left. We almost did not recover from that. We are still recovering from that. And suspicions that I thought that I had buried, are now back in full force.
So while a WS may do, say, and show love during the time that they are still lying, when that lie comes out, all trust in what has happened before can abruptly die.
Glad that you guys are having these heart-to-heart discussions!