If one observes sneaky or strange behavior- that's a green light to learn everything needed. The sneaking person legit can't justify being mad they are being investigated. Shows partner gives a damn- if partner dislikes the "snooping" I'd suggest the snooping individual breakup with the one being looked into.
Yikes. Such toxic mentality here. Snooping is an invasion of privacy regardless of how your partner is acting. If you partner is acting strange ask them directly. If you have a problem with them not answering, break up. Snooping is scummy and low. How can a relationship continue healthily once trust is broken?
Look out Aeonian, you're boyfriend thinks strange behavior is a green light to ignore boundries.