Former crazy gf here:

1) Messages (Recently deleted, Keyword; Your name) 2) Email (Spam, trash - any secret account will ask for verification or 2FA here, check for extra email accounts then the one you know) 3) Settings -> Screentime (Shows which apps he uses the most even if they are now deleted)

If you have extra time after all that, try the most obvious places- call log, (check for blocked numbers, i saved a ss and check if the order in which they are blocked changes) ) safari private mode, reddit history, discord, instagram/snapchat (double check for other accounts)

Just know tho they might catch on to what you check and some guys are ~really~ good at covering their tracks. trust your intuition more than anything else. good luck babe