This was a story from an anthology. A man is trapped in an alien blob on a planet. I think his mom or some team member tries to rescue him, by the time she manages, he is so happy living inside the creature that he does not flee with her. By that time he looks like a blob himself. And I think the mother dies and he doesn’t care.
It was just those two people finding the creature, maybe one more to demonstrate what the creature does.
I checked every blob and absorbed and mother post, no luck.