Whether or not it will help is largely dependent on a host of factors that are personal to your situation. It can help, or it could not. That depends on you, him, the outcomes, and what each potential outcome would mean for your ability to trust.
I only have experience with the polygraph. My WW wrote out a timeline. I did not/still do not believe that it represents the whole iceberg. So I constructed four questions to catch lies, omissions, totality of sex acts/ and if coitus occurred.
She passed the polygraph. Things were easier for a time, but it gave her ammunition to act like we were past this.
I discovered a menagerie of information I didnt know about from electronic snooping that threaten, but not destroy, the veracity of the polygraph. Essentially, to me, the whole timeline is in question again. She has a passed polygraph to lean against revisiting disclosure. And rebuilding trust might not be possible for our situation, at least not to my satisfaction.
But your situation might differ. Your wayward might not have lied for as long as mine did. I cant afford to impose my conclusions on your relationship. You could derive trust from your outcome, circumstances depending. My view is its worth a shot, a chance. But it isnt guaranteed to be your magic answer to the trust problem. Id advise you to be prepared for that possibility.
Polygraphs create a binary outcome. Either deception is detected, or it isnt. Its possible to have deception detected for true statements. And its possible to lie without being detected. They arent infallible. A person who has fooled themselves to the point of believing their own lies might pass. Or not, and still believe themselves!
The trust has to come from you, your resonance with placing faith in him. You can try, you can get help, he can do everything right, and still. If you cant do it, you cant. Thats not your fault!