Help! New Apple ID to stop my ex-wife from accessing my iPhone?

How do I create a new Apple ID (or whatever else) to use on my iPhone 16e so it can stop being "hacked"? I know, "It can't be hacked!" Hear me out:

iPhone 16e running iOS 18.7.1. Over a year ago my wife and I split up. Another woman was involved (no, I'm not a scumbag, it's waaaay too long an explanation but please don't let this stop you from helping me). Wife was angry, stole my phone to read my texts to this other woman. She had it for 2 days before giving it back. I am bad about passwords, generally using the same 5-6 ones with maybe a question mark added or taken away, numbers added at the end, etc. BUT, I thought my Apple ID password was safe; it's not like the others.

I KNOW she has access to info on my phone. Don't tell me it can't be done; tell me HOW it's being done and how to fix it. How do I know? She's made SEVERAL references to things I sent people in text Messages that she could not have known in any other way. Example: My girlfriend and I split up in the grocery store to shop. I texted her to ask where she was, she texted back to say she was in the back of the store buying us some beer. Two weeks later when my wife was ranting at me over text, she wrote, "Are you so busy you can't even talk to me?! What, are you and your little girlfriend busy buying beer in the back of the store???" Example: I texted my gf a pic of me in some joke underwear we got on our trip to Las Vegas trip together. Some time later my wife mentioned me wearing my Las Vegas underwear. Suffice it to say, NOBODY but my girlfriend has seen me in those underwear or even knew about them. There have been SEVERAL more times my wife has referenced things she could only have known by reading my text messages.

I think she can also track my internet usage. A few months back I booked a flight to Vegas. I hadn't told anybody I was going. When my wife was yelling at me to give her money bc she couldn't pay her bills, she mentioned me "wasting money going to Vegas again." There have been other examples where she's referenced things she could only know if she knew websites I had visited or things I had bought online. I asked our adult son if he could help me with her having access to my phone, he's said she's also said several things to him that made him feel pretty certain she can see what websites I'm visiting.

Ever since I bought my last phone I got junk texts addressed to "James" (not me). For 7 years now. No big deal. Never got texts addressed to anybody else, until a week ago I got a text addressed to my wife's name. First time. A junk text, but still. Twice in the last two weeks I got a text from apps I use (banking, etc.) giving me a confirmation code, EXCEPT I hadn't tried to log into those apps/sites.

Finally, weird stuff happens on my phone all the time. I haven't noticed any unknown apps or weird battery usage, but frequently I'll just be carrying my phone in my pocket like I always do, having left it on the home screen, and when I pull it out to do something it will be open to some app I might rarely use, on a page that would have taken SEVERAL different links to get there. (In other words, it won't just be that I accidentally hit it the camera app with my finger when pulling out my phone; just as an example it will be open to Google Maps with half an address typed in).

I've changed my apple ID password a couple of times since I first suspected she was accessing info on my phone. I bought a new phone (transferring my old data and using the same apple ID, though). As far as I know I've turned off (and never used) any Family Sharing, Find My Phone, nothing like that. I've logged onto Apple Support or whatever online to see what devices have access to my iCloud (?), but have never caught her on there. Here's my concern: I want to stop this from happening, so I'm willing to reset the phone or change my apple ID, but I want to save all my photos and some of my current text message threads. Is there some way for me to do that?