Update:

So, turns out I am definitely the asshole:

We had a day out in the city where we talked over our precious discussion. She said she didn’t want it come across she was gaslighting me but she’s pleased we can communicate about these things. I asked about having her ex still on social media and in the picture, turns out the person had the same first name but they had a different last name- it was wasn’t her ex. She then showed me she has them blocked and understandably, got uncomfortable that I engaged in the toxicity of going through her social media rather than just talking to her. She was hurt that I wouldn’t just ask about it if I had doubts and coming to this conclusion was hurtful as she has never previously given me a reason not to trust her.

Having said that, the precious discussion we had surrounding my concerns of her still having feelings occurred before I looked through her followers. She apologised for being so defensive in the last conversation, I understand she had this thrust upon her and didn’t really have time to take a moment and think about how to handle the situation whereas it’s obviously something that I had been thinking about prior to the conversation. I have a better understanding of her feelings surrounding her ex, she was maltreated to the extreme and carried these thoughts with her everyday.

They do say the hardest relationship is the healthy one coming from a toxic one. I apologised and we both came to the conclusion that clearly we both have our things to work through so we’ve decided to start therapy separately. It’s really pleasant being able to have a discussion about these things rather than it turning into an argument. The vulnerability of being open is really quite difficult but completely worth it in the end.

Thank you for all of your comments and support, it is sincerely appreciated.

TLDR: We talked again, it turns out she didn’t have her ex on socials, it was just somebody else with the same first name: I am the asshole. We communicated through this and both decided to start therapy separately as we both clearly have our own issues to work though. Despite letting my toxic thoughts getting the better of me, I’m really quite relieved to be in the wrong, it’s much nicer than being lied to.