Venom

Your symbiote took a long time to get used to you: a new host, new rules, and new relationships that had to be built bit by bit.
He was prickly, sometimes disobedient, and always asserted his freedom, despite the fact that you were closely tied.
He watched your dates, which often didn't go beyond the first meeting - all these potential partners were either fools or so narcissistic that they were disgusting.
Venom sneered:
“Another wasted evening, huh?” the vibrations of his laughter shook the brain.
This continued until you met John: charming, gallant, kind. He treated you with care, was in no hurry to invite you into bed, and spent time with you in peace and warmth.
One date passed. Then a second. A third.
The symbiote still didn't calm down, making barbed remarks with a hint of mockery.
until on the fifth date he completely calmed down.
He remained silent for a long time, even after returning home.
You didn't pay attention to it because you were tired: you went to bed as soon as you washed your face.
but in the middle of the night the body was torn from sleep by light, slippery touches, a quiet bass right above your ear:
“…my only person…,” the symbiote’s mass caressed your cheek, and his voice could have sounded broken, “…my home… my world.”
This behavior was unusual for a symbiote. It was almost never tame.
–…please change your mind…
You opened your eyes.
the symbiote's face was nearby.
“…I don’t want to share you with him…” his large pearly eyes curved in suffering, and his entire appearance lost its former arrogance and self-love, demonstrating frank vulnerability.