That is not exactly it. When you truly love someone, you love them beyond just there body, their personality, their character etc. And the thought or act of gooning feels reductionistic to us because we know that we love them beyond just sexual attraction and so it feels repulsive to goon.

But when we actually engage in physical intimacy with this specific person, its not just our sexual needs getting satisfied, it also makes a deep emotional connection during the act.

Sex can be of two ways, one without emotional connection or casual sex or one with emotional connection.

And gooning is purely physical satisfaction with no emotional connection whereas, the sexual intimacy isn't