You're not imagining thing many players including myself have noticed that there is potentially a chemesty/attraction system already in place. I've had sims who even though I wanted them together if I just let them go about their own wound up hating each other and sims who just seem to get along really well and can't stop talking to each other. And it's not just with sims who I'm trying to get together I've noticed sims who are family members with high relationships (my influence) just seem to always be at each others throats and going out of their way to be mean to one another.
