You begin to enjoy the mermaid's pussy around your cock. From her moans, it's obvious, Vanessa is having fun too. Obviously, mermen have more going on below the waist than you first though.
The mermaid's pussy is exquisite. It undulates over your cock as her tail moves back and forth. It's like nothing you've every felt before. Any jealousy you have for the merman fucking your girlfriend a few yards away is overshadowed by the pleasure being administered to you be this sexy mermaid.
The memaid plants a deep kiss on your lips, you return it and probe her mouth with your tounge. You open your eyes slightly to see Vanessa and the merman in a similar lip-lock.
Your enjoyment is replaced with terror as the mermaid wraps her strong arms around your neck and twists her body (and yours!) under the water. You flail about, fearful of drowning in her embrace, but it's no use. She's far to strong and a much better swimmer than you.
As the strong underwater currents drag you both away from the shore and into the open waters, you notice that your lungs no longer burn from lack of air. Quite to the contrary, you're breathing the water!!!
You settle back in to the pleasure of the momnet, thankful that you have not drawn your last breath.
Just then, Vanessa and her companion float past. She smiles at you as the merman thrusts into her. As she passes, you notice that her feet appear strange. They run srtaight from her legs,like her ankles are gone. Her toes are spread wide, about a foot and a half across and they're nearly a foot long with a thin membrane spread between them. Their color is changing too. A deep blue green hue (similar to the merfolk's tails) covers Vanessa's feet and is spreading up her her calves.
Although you cannot see them, you move you own feet and feel the resistance of the water as if you were wearing swim fins.
The mermaid senses your dismay and kisses you again. In your mind, you hear her say. "It's okay. I was confused too when it happened to me, but there's nothing to fear."
A sense of calm washes over you as the mermaid milks your cock. In your euphoric state you smile back at the mermaid and then look blissfully toward Vanessa