By the time I found out about the phone app it was too late, and I had evidence aplenty. I started out like you actually. Telling myself I just needed a bit of solid evidence to go on.
Thing was each time I uncovered a bit more, I told myself it wasn't quite enough to go on. I was frightened you see, hence the dilemma.
I did go to a private dick in the end, after the second OW, because by then I knew beyond doubt that he had been lying and cheating for a long time. At this point, I'd had an anonymous letter, my DD had been telling me he was fucking about, stbx was being extremely cruel, and then I did manage to get access to his work mobile and there were the texts between them.
The private dick traced him to the OW's home. they can put GPS tracers on cars which show where the driver is going. It's all quite impressive really. I didn't do that though, I'd kicked him out by then. I just needed an address to serve papers to and I got it within the hour. It was an enormous shock to hear the confirmation.
You know your DH better than anyone. Your intuition is telling you that your reality is far different to the one he is presenting you with. If you deny what your instincts are telling you and let him define the truth it's not a promising future is it?
That's what I mean when I say the views expressed here are not unbiased. They are the views of people who feel you are being done a disservice by your DH, and you are, if he is failing to either provide you with proper reassurance of his 'innocence' and commitment to you, or the truth, whatever that may be.
Either way, subterfuge is enormously debilitating to live with, it saps confidence and energy.