Got an Answer?
You need to get to the core of why he is having trust issues to be able to fix the problem. Book in for marriage and individual counselling. It sounds like he may be feeling a little self conscious about something (like if he has put on weight, found a gray pube, or you aging better than him).
It’s not your job to prove you’re not having an affair, it’s his job to prove that you are. What a crap situation to be in. I agree marriage counseling can help get to the bottom of his insecurities/behaviour.