They Start Acting Nice Towards You
For some period of time, your partner becomes nicer, they open the door for you, ask you how you have been doing lately. It is completely normal if they used to act like that on a regular basis but if they suddenly start acting like that you should become suspicious and for a good reason too.
You need to find out what has brought this change in their behavior, which is why you must take your time and observe things around you. You have surely heard from people about how their partners had cheated even though they didn’t expect it from them. They acted like they were the salt of the earth and suddenly you come to the realization that they were sleeping with a colleague at work.
Being overly nice and courteous is a great tactic to divert the attention away from them in order to distract you from thinking that they are cheating on you.