With your indulgence, I will briefly list some behaviors/incidences surrounding the "big three" moments and ask only one more question.
First time: 1. Became highly protective of his cell phone and his email when he had always left both open/ lying around until then. I would call it obsessively protective, denied it was true, but began hitting the bathroom (with his phone ... to delete recent texts?) as soon as he walked in the door from work, which had not been his normal routine before, nor was it his normal routine after this episode passed.
2. Simultaneously became somewhat disengaged with me and off inside his head somewhere in the evenings, as though processing thoughts or memories.
3. Was unaccounted for while I was away for a weekend during this period; I had unidentified objects in my house when I returned, that he couldn't explain.
Second time: 1. He began talking with a new "style" of speech, or accent, I guess (like junior high girls might do) along with espousing atypical, IMO immature, opinions and soundbites about life philosophies, which stabbed me in the heart with an "Uh oh, not again..." feeling.
2. A younger female from his workplace that he described as a "long time, close friend" but whom I had never heard of (I had met almost everyone he had ever termed a friend from work or otherwise), insisted on meeting me before he changed to his new employer. We all went for drinks - her, her girlfriend, him and me - they sat next to each other, laughed about private jokes, nudged each other's shoulders, he actually acted jealous as she went on about various men (so who was that? when did that happen?). I couldn't believe what I was watching and hearing. Even the friend seemed to feel sorry for me. The first time I excused myself, this chick jumped up and followed me to the ladis' room and started asking me "I'm trying to get to know you" types of questions. It was surreal. My BF's explanation... she's just a friend. And not that good of one. In his final week of work there, he had what appeared to be (compared to our usual emailing habits) one afternoon's absence from the office, returning at about time to come home and two days later, one three and a half hour late arrival to the office, though he left home on time.
3. After his job change, he joined her health club, but dropped out after the first month.
Third time: 1. He suddenly, inexplicably, began coming in from work a little late, every single day. twenty minutes, thirty minutes, forty-five minutes. After a week and a half of this thing that he had never done before (having always been one who could not wait to leave the office, as long as I've known him) I asked what was up. He said people keep coming in his office wanting him to check on things and he can't get away. I questioned why suddenly, why never before, why every single day all of a sudden? What he did not tell me, and I didn't know until months later, was that he had a brand new office mate, a non-permanent employee who was sitting in a previously empty desk in his otherwise private office. She worked later hours than he worked. After our initial conversation, he started coming home on time again some, late some, but blaming it on traffic now. Then came the big moment, over an hour late the day before our long-planned four-day trip. A call he wouldn't answer on his cell the next morning on our way to the airport (it's the office; I'm not answering that). Undivided attention to me that made me feel like royalty - almost overdone? - during our trip. A few more late days at the office thereafter, then no more. Then some gradual bitching about the new woman they stuck in his office "a couple of months ago" - NO WAY would I have not known this under more normal circumstances - then he gets her moved out to sit somewhere else, on another floor, even. All of which I hear about, as usually would happen.
As you can see (I hope) my feelings at least have a reasonable basis. But he very elegantly, heart-felt-ly, but sometimes angrily, argues his innocence.
So here is my question: provided everything I feel is true and he is a dishonest cheater, would CBT still help me just the same, or would it possibly lead me to sticking my head in the sand in a way that might be detrimental to me?
I'm not trying to save this relationship so much as work on problems I might have that I'm not recognizing. As stated originally, I'm ready to let this go and move on.