Go home and change.

"Sorry." You say. "I'd really like to have a bath with you but I'm just not comfortable with crossdressing."

"Okay." She is clearly disappointed. "Can you do something for me though?"

"What?" You ask.

"Can you wear a diaper under your clothes tonight?" She requests.

"Why?" You remember thinking about trying one last night. You worry that somehow she knows that.

"I've seen you looking at my butt, trying to make out the diaper. I know you can't stop thinking about the fact I'm wearing it." She explains. "I thought if you were wearing one too then we could move past that."

"I'll think about it." you say.

Sarah sends you on your way with one of her diapers in a, thankfully opaque shopping bag.

You get home and shower then look at the puffy white disposable diaper sitting on your bed. If you're going to wear it, now is the time.