No, this does not actually come in a nice little box.
If you don’t have $2000 bucks to shell out to a private investigator every 2 weeks, AND you are resigned to dig and dig around for more information on your cheater instead of being more productive with your time and your precious life, like working on a plan to walk away from your abuser, then here are some tools that can be used to bit by bit gather those painful nuggets on your gaslighting scum of a spouse.
The idea here is to find out what you need to know from piecing tidbits together. A little from the GPS, a little from the recorder, a little from the phone if accessible, a little from computer history and a little from, yes, his/her underwear. This is tedious and exhausting especially since you have real responsibilities as well, like parenting, or keeping yourself gainfully employed, shopping, cooking, laundering, etc…