Well, as far as pure chemistry goes…
I was with a guy for three years. We didn’t have a lot of chemistry to begin, but we were in a long-distance relationship for a while, so we got to have sex only rarely.
Eventually we moved in together, and it died off quickly. We would sleep naked together, and feel nothing. On the rare occasions that we had sex, it would just be non-affectionate, no kissing, pretty much to get off so we could go to sleep. Afterwards, I’d wake up, feeling kind of icky, like one might feel after having sex with her brother.
Kissing him was particularly weird, weirder than sex, since the smell of breath and breathing his recycled air was just too difficult for me. It really did feel weird.
It was not a negative relationship, though. I love his personality. I sometimes think that if I didn’t have someone else and he asked me to marry him, I’d say yes, because it would be so nice and comfortable.
He remains a very good friend of mine, of course - one of the best! We just don’t have any desire to touch each other.
I don’t know if this counts as negative chemistry or not - I wasn’t repulsed by him really, I just had this icky “whoa, I just had sex with my brother” feeling which would pass quickly. And I didn’t crave sex with him, it just sort of happened sometimes.
Apologies for any… non-sense-making-ness. I can’t even think of the real word I’m looking for. 7:30 am and I haven’t slept? I need to go to bed.