1. They Take Longer and Longer to Call or Text You Back:
Taking their privacy away is something you shouldn’t do, but if they take advantage of your trust on them then they are either a terrible person or they think you are stupid enough to trust them blindly.
If they take too long to text you back or return a call, then there are chances of them cheating on you. In the dating period, you get to know how quick they are at replying to your texts and how long it takes them to get back to you on a phone call.
If that is changed and they deliberately take hours to text you back, there is enough space for doubt to arise. It does not take too much time to reply to a text and even if they are actually busy, it won’t be once or twice. Repetition of late response is a sign for you.
Adding a screen lock to their phone is another sign.
If you have never tried to unlock their phone to read their conversations and check their call logs, why is it that they suddenly felt the need to lock their phone? They clearly want to hide something from you, and that ‘something’ can be a ‘someone’ they are fooling around with behind your back.