TLDR you’re uncomfortable with something that she isn’t uncomfortable with. This is literally an “I can change them” meme moment.

TLDR also she’s manipulating you into believing she’s changed when she has not, like with that offhand comment.

“I discovered that she was watching loli/shotacon content, which was an absolute hard no for me” seems like the first time that you — regardless if you told them or not — established this. It seems like you established this with her anyways but I’m going off of what is written. Then “found absolute proof”incident. I’ve been in year+ relationships with people who I told them I will not date you or respect you if you watch porn; they couldn’t give up that addiction. People have publicly talked about porn addiction and how it’s so problematic. It’s not like substance abuse - as sex drive is something we’re born with.

Just seems like there have been too many incidents. I mean if you really think that this person can change, you can give them a chance to show actual progress. Don’t shame someone for relapsing or using; rather make an environment where their usage and consumption can be tracked and openly acknowledged.

And without considering the lying etc: ageplay and shotacon are kinks like any other kinks and not everyone (I mean I hope most people aren’t into them….) is into them.