The manga isn't doing a good job of explaining this since a lot of it was internal thinking, but apparently dominant alphas in this world like ML have an extra appendage that comes out of their junks while knotting. It keeps "attacking and licking the [omega's] innerwalls" when their junk gets so swollen it can't really move lol. So anytime MC is like, "WHAT IS THIS STRANGE FEELING" it is because there is something (he describes it like a spongy tongue) that makes him feel so good he is overwhelmed. ML knows about this but doesn't want to outright tell MC because he saw the appendage once and it was pretty ugly and he doesn't want to scare the MC. He is pretty self-conscious about it.
The manga isn't doing a good job of explaining this since a lot of it was internal thinking, but apparently dominant alphas in this world like ML have an extra appendage that comes out of their junks while knotting. It keeps "attacking and licking the [omega's] innerwalls" when their junk gets so swollen it can't really move lol. So anytime MC is like, "WHAT IS THIS STRANGE FEELING" it is because there is something (he describes it like a spongy tongue) that makes him feel so good he is overwhelmed. ML knows about this but doesn't want to outright tell MC because he saw the appendage once and it was pretty ugly and he doesn't want to scare the MC. He is pretty self-conscious about it.