Many times, the cheating partner can start to become overly sensitive over his/her non-shared personal items such as their phone, car, or living space.
For example, if before he/she left their phone out while taking a shower, they may start to bring it into the bathroom with them or become very agitated when their significant other asks to look at a funny video or something else on the phone.
Full article here: https://hernorm.com/how-to-spot-a-cheating-partner/
