Gofushi and Sukufushi are both possessive as fuck, but the core difference between the two is how they trust Megumi. Gojo is possessive of Megumi, but he has to do everything he can to keep Megumi with him because he can't trust Megumi to stay with him if he's given a choice.

He'll block off all his friends, family, manipulate everything in his power to keep him by his side, because he can't trust that Megumi would see himself as an option so he has to make himself the only one Megumi can rely on, regardless of the truth to that.

Sukuna, meanwhile, has so much trust in Megumi, because he sees him as capable, and isn't afraid to lose him because he already sees him as his.
He doesn't need to take away his options because he knows Megumi will come to him on his own without fail.

Gojo, no matter how long he's been with or been through with Megumi, can never get that level of trust, because he's only seen and had Megumi as a possession he could play with so long as Megumi believed Gojo was the only one who'd take him as an option.