Girlfriend (30F) of 4 years is obsessed with the idea of loyal me (32M) possibly having an affair.

I love my girlfriend dearly, and while I have made boneheaded mistakes and owned up to them like any responsible guy would, I have never been and will never be disloyal to her. We both entered our 30's together, we have even lived together for a year. Overall, I believe we have been a solid couple, and on a foundational level, love each other very much. We have been through thick and thin, we speak each other's love languages, and we know how to resolve conflict. I've made clear that I want to spend the rest of my life with her, and we're both ready to seal the deal once the timing is right due to potential career changes and uprooting.
Over the past six months or so, something has changed. Communicating with her has gradually become more difficult, and she has trouble maintaining eye contact with me, and distances herself from me. She regularly questions where I am and who I'm with. Every time I speak with her, and show her evidence of my day, I still feel a constant air of suspicion from her - an "Oh really?", a raised eyebrow, so on. Even in the middle of a weekday, where there's nowhere else I should be except at the office, replying to her that I'm at my desk doesn't seem to satisfy her curiosities. Having a platonic interaction with any other woman causes my girlfriend to raise defences, questioning how I know them and that I must be attracted more to them than her.
Then there's her recent entertainment choices. Her books, music and podcasts, films, and socials are full of love affairs, web sleuthing, true crime, romantic comedies, dating reality. Whenever I walk by or tune in with her, the general theme is how terrible men can be. I feel like she's falling down the same kind of rabbit holes you hear about conspiracy nuts falling into. Her algos are definitely encouraging her state of mind.
Intimacy has crumbled between us. She barely wants to hold my hand. I hug her, and can feel her being physically repulsed. Flowers, her #1 favourite gesture, are no longer adequate. I know she has her own abandonment trauma, and I have been very patient by either navigating it with her, or giving her space when appropriate. I've brought her with me to couples counseling, but in her mind, my eagerness to repair things is an admission of guilt for adultery that never happened. This week, after four sessions, she decided to stop going with me. That is her choice, and I will continue trying to be positive and supportive, while clearly expressing how troubled I feel.
I want to work this out, I want to know where this all stems from, and why she suddenly trusts me so little after being with me for this long. Instead of offering some transparency in return, she continues to be the victim, continues to criticise me, when I feel her state of mind is hurting both of us equally. What else can I do to show her that I still love her to bits, and we can still be the loving, trusting couple we were not too long ago?
--------
TLDR: My girlfriend is obsessed with the idea of me cheating on her, even though I haven't and will never do so, and have never shown behaviour that supports her suspicions, and I'm beginning to worry about losing her if this is all beyond my control.


Source.