Basically the title. She's been having problems every time we have sex almost unfortunately. We are both tested and don't have any STDs and are honestly both very clean hygienic people. But yeah because of her problems down there, we have stopped having sex. I've heard about people's bacteria evolving or just not meshing well with each other before so I wonder if that's possiblly happening between my partner and me.

Her last fuckbuddy, she and him had a very strong physical and sexual connection. Maybe even biological because he came inside of her (I have video and picture as proof lol) and she didn't have any issues at all afterwards. She hasn't slept with him in a while. Since then, I have been her only sexual partner but she started frequently having problems down there when we have sex especially when I cum inside her.

What started as me not cumming inside her anymore evolved to wearing condom into just repressing my sexual feelings and masturbating on my own. I don't want her to feel pain down there. But I keep thinking about her old fuckbuddy. When she decides to fuck him next, I might just encourage her to not use a condom. She might just pressure me to let her fuck him raw anyways knowing I won't say "no" because she knows how much this turns us both on. It turns me on more knowing she wants him and her body loves his cum whereas her body just rejects my cum and we can't have sex for a while afterwards... maybe we will see of she has any sort of problems with future guys. For now we just know there's one guy who can cum inside her and she has zero problems.

Is there any merit to this idea that some people's biomes or whatever just don't mesh well with each other? And that some people's germs might react well with another's?