You swim over to the edge of the pool and nervously greet her.
"Uh, hi Caroline, have trouble sleeping?" you ask.
She walks over to near the edge of the pool. She's wearing a long bathrobe tied tight around her. "I thought that was you. I heard splashing and you weren't on the sofa so I figured you had decieded to swim with your new mermaid friend."
"Yeah, it seemed like a wonderful night for a swim. You should dive in too."
"Come on in Caroline - the water's fine!" suggests Topaz. She playfully splashes Caroline with her tail.
"Oh well now that you've gotten me all wet I suppose I'll have to" responds Caroline with a playful grin.
"I should probably let you know I'm skinny dipping" you say.
You're happy to see Caroline continues to smile. "But of course - that's the only way to swim at night!" She unties her bathrobe and lets it drop to the ground to reveal she is wearing nothing underneath. You've never seen her naked before and you're certainly enjoying the view.
Caroline dives in and kicks off for the far end of the pool. She's clearly a better swimmer than you were as a human, probably because she makes plenty of use of her pool. You deciede the time is right to break the truth to her. You propel yourself after her with powerful strokes of your new tail. You dart around her, swimming around her fast enough to prevent her from getting a good look at your tail.
She surfaces in the shallow end and looks around for you "Wow, Neil, I didn't know you were such a good swimmer!"
"I wasn't until very very recently." You splash her from behind. She turns around in time to see you splash her again with your tail.
"Neil! Since when did you have a tail???"
You slowly circle her, admiring her body. "About the time I became a better swimmer." You take a deep breathe and go for it. "Caroline, I don't know if you think of me as just a friend but I love you and want to be with you. Make love to me and join me in the new life Topaz has opened to me."
"Stop circling for a moment!" You come to a stop in front of her. "I know I've been emotionally distant sometimes because of the divorce but...oh god yes!" She plants a massive kiss on your lips and you pull her into an embrace. You soon take her to the bottom of the pool, where you find your manhood ready to emerge. She wraps her legs around your tail and you take her to new levels of ecstasy.
Out of the corner of your eye you see Topaz looking on, but you couldn't care less about your audience.
At last the two of you drift back to the surface. You cuddle as you float together. "So what happens now?" she asks.
"You join me and Topaz."
"You mean..." Caroline begins but is cut short as her changes begin. Soon she has a tail almost identical to Topaz, but a lighter shade of blue. After her tail has finished forming, Caroline gives it a few tenative kicks. "Oh this is so wonderful."
"I'm glad you two are enjoying but how are you going to fulfill your part of the bargain now?" asks Topaz sounding angry.
"Bargain?" asks Caroline.
"She offered to turn us into merpeople like her if we returned her to the sea" you explain.
"And how are we going do to that now that we all have tails?" Caroline demands.
"Ummmm...I didn't think of that..." you admit.