Have you continued asking to bake with Rosy? Grab her ass each time (the first time can be when you bring her flour to re-open the bakery). The first grab-ass gets you a kiss. Later ones are showing her tits, showing her pussy, giving you a BJ, and eating her out+getting a footjob; the last two require a special pastry each. After oral+FJ asking about him unlocks. Since you have the key you can progress immediately through 'The Missing Boyfriend' to 'Comfort Rosy.'Hm, I seem to be missing some activation trigger for Rosy. She never told me about her missing boyfriend. By now, I actually found the skeleton and key already but still can't progress her. Any ideas?
Not sure if her Affection needs to be high enough for that, though. I always buy a pastry daily, which is an Affection bump plus useful for topping off HP, and take my time with her since it'll be a while before you get the key. You can max her Affection out just by buying pastries, but baking is needed to progress her storyline.