TIFU by using my girlfriends apple ID to start our new ipad

I (34M) recently purchased a new iPad for my girlfriend (33F) and I to share. I am not a big apple person and so don't even have an active or known apple ID. So when I went to set up the iPad I asked my girlfriend for her info. She happily gave it to me and went about her business. I proceeded to log in and it said it was going to take some time to set up so I walked away.

I came back and started poking around the iPad. I suddenly saw text messages, photos, and all sorts of things on the iPad. I was confused at first and then realized apple must have downloaded everything from my girlfriends cloud.

I fucked up by not just telling my girlfriend about it and us figuring out how to remove the stuff. We have had a good relationship but like all relationships there have been rough patches with both of us needing space. My girlfriend was also on the apps before we met (we met through work) and so I knew she had a lot of partners. She had openly told me about some of them and was pretty much an open book, or so it seemed.

I saw the texts load on the iPad and I just couldn't help myself. I started reading. And reading. And fucking reading. The texts went back YEARS. Now a natural sane invasion of privacy would to have got to the point where we started dating and stop. But I didn't. I read probably hundreds if not thousands of her messages. There were a few sets in there during our relationship, including when we were having rough patches, that made me a bit upset but nothing that indicated she went further than a flirty text. However, it was the before the relationship ones that really blew my mind. She had hooked up with a number of our coworkers (I only knew of one) and had lied or at least obfuscated the facts around two of her past relationships. Moreover, she absolutely had cheated on at least one past boyfriend. Something she said she would literally never do to anyone. She was texting a ton of guys at a time and often misleading them that she was exclusive with them.

After going back about 2 years of these texts I stopped. I became so confused and conflicted. Literally before I opened this iPad up I thought we knew each other very well and that we were happily getting more serious (we are planning to move in together officially very soon). But the person I saw in these texts is not the person I see sitting across from me everyday.

I haven't let on to her that I now know every sordid detail of her texting life for the last 2 years and I've tried to be myself around her. But everything I read is nagging at me hard. I wish I had never seen that stuff and just blissfully existed with my limited and catered version of my girlfriends past. I guess this is karma for reading it all. If I end up confronting her about it, I will post an update here.

TL;DR: used girlfriends apple ID on new iPad and it downloaded her whole life and I went from blissfully happy to doubting and troubled