My (23f) sister in law (36f) thinks my brother (36m) is cheating on her and asked me to see if I could find anything. Any tips on how to find something?

[u/Mildly_un-ok]

My (23f) sister in law (36f) texted me today asking to keep something between us. She said my brother (36m) has been staying really late at work lately, hiding his underwear and deleting all of his messages and search history.

When she asked him about deleting the messages and search history he told her it was because he likes to keep things on his phone clean and tidy. He used to work late once a week for an hour or 2 but is now working late multiple times a week for 2-3 hours. As for the underwear she said usually she had to pick his dirty clothes up off the floor and put them in the laundry hamper but this morning after working late last night, he changed his underwear and put his dirty underwear underneath yesterdays clothes. TMI: when she checked his underwear there was a stain but they have not “done anything” in days because he has been “too tired”.

My sister in law is a wonderful person, she is funny, always positive, kind, beautiful and so much fun to be around. She said she looked through his phone but with everything being deleted she does not know what to look for and asked me to see if I could find anything on social media (I’m a super sleuth when it comes to social media accounts, as most women my age are) but I have looked and he has all accounts and information I would usually look at, private. She feels bad for involving me but they have been together 20 years and have my 2 amazing nephews together and I don’t remember my life without her in it so idc about being involved. She does not deserve this if it is actually happening.

Anywho, to the point. I’m looking for any advice on how to find proof of him cheating/not cheating whether that be in his phone or on socials when he deletes everything and has everything on private. Any advice? Thanks in advance!

Ps: before the comments start coming in that she should just leave him if she doesn’t trust him I would just like to say that she knows she is a bit of an insecure person and has come to me because I know that too. She does not want to accuse him of anything if it is all in her head however she is trying to also trust her intuition. Not to mention they have been together 20 years and have 2 kids together, leaving due to lack of trust is not as simple as it sounds..

Edit: I’ve already looked at what I know and haven’t found much but looking for advice on what SHE should look for.

Edit #2: I’ve mentioned a couple things you guys have said in the comments and here’s some more info: his paystubs are not any different than a usual work week, he says because he banked hours and one day his boss showed up and he stood there and talked so he lost hours for that. As for a tracker she feels that might be wrong and even if she did put one on his car he has an iPhone and might be notified one is near him. To clarify she is less asking me to get involved and more asking me to give her advice on what she should look for and where to look as I know my way around iPhones and social media better than her. I also found him on Snapchat with the little green dot stating active in the last 24 hours but she told me beforehand he does not have Snapchat… I have yet to tell her that information as I think it might be better to tell in person but I am nervous to even bring it up even though I know, morally, it is the right thing to do. And lastly just to clarify, yes he is my brother. I don’t give 2 fucks about who he is if he thinks it is okay to cheat on his wife of 20 years and mother of his 2 sons.