as you and Jason started to make out to start the sex involved in this orgy like all these other merfolk couples, a selection of mermaids suddenly break loss and pull Jason away from you and as this happened their former mermen partners pull you into their group.
confused by this sudden action you were then surprised even more when you saw Jason willingly embrace one of the mermaids yet before you could complain one of the mermen embraced you and allowed their massive cock once hidden to penetrate you, somehow completely erasing the jealousy over being cheated on.
the feeling of this fish-man's cock was amazing inside you, and proof merfolk really could mate without taking human form. if the mermaids were just as exacting to Jason and this was part of some plan of his then why now fight it.
but then terror overtook your joy as suddenly without removing his cock from you the merman you were having sex with dived down taking you with him and swimming away from the shoreline with Jason and his mermaid partner doing the same as were all the other merfolk in now new sets.
but oddly instead of your lungs bursting or your consciousness fading from a lack of air, your body was now processing the water like it was air, then you caught a glimpse of Jason as he floated past with his partner and noticed his toes turning into branches almost like the webbing of the merfolk tailfins, noticing your confusion your merman partner spoke "relax lovely, it comes as a massive shock at first as the mating process converts human to merfolk... but fear not, no harm will result in it"
as he finished the merman finally left you but then another took his place, repeating the process, the mermaids doing a similar switch with Jason that momentarily returned the jealousy but it faded again: