@crinrict
My Sim was female. I was hoping to get her to have a baby with the Flower Bunny, but I found out as I was about to have her make their relationship official that the Flower Bunny was female (must be random). I know this because it said "ask to be girlfriend." Upon discovering that, I enabled testing cheats and edited the Flower Bunny to be male in CAS. Could this be what caused the problem?
Then again, I'm also not sure if the Flower Bunny's sex is supposed to be random, or if this is a bug and he was supposed to be male. I'm also noticing that, for some reason, despite being an adult and having a third trait slot, the Flower Bunny always only has two traits, Bro and Cheerful. I don't know if that's by design as well or not. I'd personally suggest Loves The Outdoors for the third trait. It would be nice to have some official input on that.