Few things are hotter to me than two girlfriends getting fat together. Not on purpose, but just by pampering each other and enjoying the good life a little too much.
Imagine them going out on dinner dates. Cooking romantic meals for each other. Their bodies becoming curvier and softer because of that and all the lazy mornings. All the evenings spent doing nothing but sit on the couch and cuddle while watching silly movies they're not even truly paying attention to.
Imagine this going on for a few months. Imagine them only noticing the effects this slow and happy life has had on them when their arms grow plumper. When their bellies press against each other whenever they hug. When the outfits they wore on their first dates start feeling too tight. When straddling each other's hips becomes increasingly more difficult.
And the best thing about it is that neither of them cares. They're too busy being happy and in love to worry about what anyone else thinks.