Would I be wrong for leaving my girlfriend because she out of no where said she wanted an open relationship?

Anonymous
Going to keep it really short without details.

I (41m) had been together with my girlfriend (38f) for 3 years. Stable relationship and no red flags from my point of view. Last Saturday she asked for an open relationship. Her reasoning was we did not get to enjoy ourselves in the past & it could help us strengthen the intimacy and love.

I rejected it and she seemed unhappy after that. I am not going to lie, an open relationship suggestion out of nowhere is a huge red flag for me and means probably there is someone else she have in mind already. I have been cheated on in the past and made it very clear that I want a monogamous relationship before being exclusive. Her suggestion made me mental for few days.

I want to break-up with her. I do love her but she opened Pandora's box and I am not sure if I can trust her in that relationship. It will not be healthy for both sides.

Would I be wrong if I leave the relationship without trying to salvage it? I tried saving my old relationship when there were trust issues and it did not work. I just do not want to harm my psychology struggling. At the same time I doubt myself because I love her and it's a 3 years old relationship.
Would I be wrong for leaving my girlfriend because she out of no where said she wanted an open relationship?
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