Once the trust is broken over and over,he is who he is.
So, my answer would be no, I wouldn’t want to continually be questioning everything he said or did.
I did that for too long when I was married and never knew what the underlying problem was in our 32 year marriage.
Life is so much better with him not in my life.

Maybe it's just due to trauma bonding and confusion, but it seems difficult to discern the motives of a self-proclaimed "gay" spouse. Are there any valid or healthy reasons they would decide not to pursue the gay lifestyle they thought they wanted/needed?

I think it was phoenix who once said that deciding between wants and needs can help gain clairity. Is having sex with the same sex a want or a need for your spouse? Is monogamy a want or a need for you?

I certainly can't tell you what to do or what is best for your life and situation. I will however, share with you my story. I have been married for 27 years to my husband, which we are now in the process of divorce. I found out about 7 years into our marriage about my husband same sex attraction and anonymous sexual acting out. At that point he swore he wasn't gay just same sex attracted and we went to counciling and groups and stayed together. I believe my husband has always been attracted to me as well and our sex life has always been good. At that point he commited to momogamy with me and approx 5 years later I found out again that he was participating in same stuff. We seperated and again did counciling etc and got back together with promises of faithfulness to me etc. Again, approx 3 months ago I found out that these behaviors were happening again. With my husband there is never any clues, it's always just a gut feeling I have and it comes out later. He is a great husband, father, partner, sexual relationship, etc. This last time I said no more I can't continue this cycle. 
Looking back over the 27 years now. I don't feel he was ever faithful to me, I think there were times he really wanted to be and tried to be but couldn't do it. I too, thought maybe I could just live like this my husband would be all for that, but then I knew that I couldn't do that to myself that I wanted and deserved more. I knew I had to love and respect myself enough to stand up for what I knew and believed a relationship/marriage should be. I knew if I just accepted and stayed out of fear and convience and security that I would die inside knowing that it wasn't going to change and that I was living a lie. 
I don't have the answers for you, but I hope sharing my experience will help you in your life. I completely understand your battle. 
 

Mine, like many did promise this.  But after over 20 years of cheating at intervals I was just so devastated by the betrayals that trusting at this level after such a long history was not a possibility.  I asked him to tell me about his journey and the betrayals, but he wanted my silence and for me to be complicit in the silence.  I could have 'saved' my marriage, but the price was for me to ignore the pain I was in at the betrayals.  I just couldn't do it.  And he was silent too often and living in another town.  I actually put a key logger on his computer and he googled male massage within a week.  I should have waited for more evidence, but I confronted him only to have to hear more denials.  The trust was gone.  The openers and intimacy I had craved for so long were never going to materialise - even if he was monogamous.  I was just too devastated to put effort into the relationship knowing how long he had hidden and deceived me.  

No I wouldn't, nor would I recommend anyone does if there are serious signs TGT.   A friend of my mother's daughter has a husband who has admitted to being gay and they have tried for five years with intensive counselling to save their marriage, but have finally given up.  My mother says "aren't you lucky he let you go"!  And I have to say that probably yes I am.... It is harder when they keep trying to deep six all TGT brings out onto the table.