You're wet with anticipation even before your girlfriend's tongue slides into your slit. You moan as she begins to pleasure you, all the while grinding herself against your mermaid tail. You've never felt anything like this before. She explores slowly at first, slowly deeper and more rapidly. Your tailfin starts flapping uncontrollably. Her hands are on her hips, her legs scissoring your tail, riding your waves of pleasure. You feel your first orgasm as a mermaid, more intense than anything you have experienced a man. Your girlfriend keeps going, delighted by the response she's getting. Your moans turn to screams of pleasure and you nearly black out from the ecstasy.
Finally, you body stills as the orgasms finish. You lay on the bed, drenched in sweat and out of breath. Your girlfriend flops down on the bed beside you. You can see how swollen and wet her clit is, but she hasn't been able to get herself off yet. Then you feel your tail separating back into legs, your transformation apparently ended by your orgasm. As soon as your transformation is complete you know you want to pleasure your girlfriend and help her get off.