Miss sunflower 100% loves and cares for Matsuri a lot, but we've had no real indication its romantic- that doesnt mean it isnt or cant become it though.
You’re right, that’s the big question—what is Miss Sunflower’s relation to love, romance, and/or physical intimacy? We do know that her attraction is toward women, based on her love for the first Miss Sunflower. We also know that she’s been opening up emotionally, specifically because of the influence of Matsuri.
(Again, as an introvert myself, I can’t stress enough how much Miss Sunflower’s statement that she gets tired being with other people but not with Matsuri says about their compatibility, whatever form their connection ultimately takes.)
My guess is that after a moderate timeskip—say, when Matsuri graduates from university—we’ll see them still being together, but whether as a romantic couple or just as people being together I cannot say.