A few hours after drifting off to sleep, you are in a deep sleep. The symbiote notices that and decide to take advantage of it.
The black speedo around your crotch starts to shift and tighten around your penis and ass like a second skin. You let out continous soft moans as the symbiote around your cock starts pleasuring you by wrapping the tendril around it and stroking your up and down until precum is leaked from your penis.
Not wasting so much time, the black speedo becomes slime and starts separating your foreskin and plunge itself into the piss slit. It gives you so much pleasure that you gasp upon its invasion, but you are still sleeping, not noticing the slime entering because you are having a dream about sex.
Then you unconsciously reach a climax and start ejaculate spurts of cum but they all got absorbed by the slime as all of the slime completely enter your dick. The black slime shifts a bit in your dick and decides to rest there. From outside, the penis got a lot of black veins surrounding the penis as a result from the latex entering your dick. It also growing an inch bigger than before.
In the morning, you wake up feeling so energetic and a bit horny. You take off the blanket off and see the erected dick sticking out with many black veins around it. You knew the symbiote is in there.