I think that if you're going to delve into 'are they REALLY faithful' absent a particular cause or causes for suspicion, you're diving down a rabbit hole of teasing apart every action they take for evidence of unfaithfulness. Like a conspiracy theorist, if you look that hard at seemingly innocent actions, you're like to find things that increase your suspicion for psychological reasons. You can always find discrepancies if you look hard enough because no one is perfect.
I'm not anti-Christian. I'm anti-stupid.