If you're bound to snoop, there's something in the relationship going unaddressed.

For instance, intimacy could have ended for months or weeks, add an argument or something to the mix, suspicions rise. Another could be, having a jealous spouse, constantly accusing, leading to the accuser having their privacy violated...there's tons of probability.

If you have to check, there's something missing. And if you leave a papertrail...best wishes...