It would really depend on the owner of the said social media account or email. If they want to let their loved ones in their account then well and good. If not, then those loved ones shouldn't feel bad even if they're their spouse. It's not a matter of getting caught cheating, but more along the lines of privacy. Even if you're married or kiving together with someone for a long time, you're still enttled to you privacy. And of course, at the cornerstone of every relationship is trust.