This is a perfectly understandable way to think. When your loved one has an affair, it shatters your trust, self-esteem and confidence, and you find yourself wanting proof of what you previously took for granted.
There never can be proof, of course, only trust, and I suppose the best way to create and maintain that trust is to talk, openly and frequently. We may also need to say and hear things that we'd rather not. For example, "The truth is, I'd like to have sex with another person, but I promise I never will," rather than the obviously false, "No, certainly not, I'd never want to have sex with anyone but you!"
There is an organisation called The School of Life (I'm not in any way affiliated with this organisation, other than being a subscriber) headed by a philosopher called Alain de Botton, and a lot of what he talks about is sex and relationships, and he's quite realistic about it. He talks about Romanticism, and how it has created the ideal of being in love with, and having sex with, one person for the rest of your life, and how this concept would have been considered strange in other times, due simply to the fact that we didn't live long enough to worry about it, or our lives were so hard that we didn't have time to ponder it!
I adore my wife but, due to her past infidelity (and other reasons), feel like I'm struggling in a swamp at the moment. The post-affair life is incredibly difficult. The daily problem I face is that I have to pretend to be fine. Our partners are very sensitive to changes in behaviour*; for example, today, I just want to wander off on my own for a few hours, but this will appear strange to my wife, unless I tell her why. But how do you say, "I've been miserable almost every day for the last fourteen years and I just need to stop having to pretend for a few hours. I'll be back in time for Coronation Street**."
Apologies for making this somewhat about me. The ground has been taken away from under you: it's not surprising you want your WH to be tested: that could help, to some extent, to rebuild the foundation of your relationship.
*Ironically, when my wife was having her affair, I noticed no change in her behaviour, apart possibly from one very memorable and deeply unpleasant occasion.
**Famous British soap opera. I'm in England.
[This message edited by Eric1964 at 7:29 PM, Monday, October 7th]