I find it fascinating that no one can really explain the Church’s stance here. We can go on and on about gravely-disordered lusts, feelings, etc., but if there’s no real catechesis it all flounders.
The subject only brings up more confusion and questions than real answers. I cannot understand why smoking is not condemned with masturbation (or why masturbation isn’t accepted with smoking), because they’re both exactly the same sort of act. One is a grave misuse of the respiratory faculty, and the other is a grave misuse of the genitive faculty; conversely, one is a harmless attachment to a passing pleasure, and the other is a harmless attachment to the occasional release of sexual tension. It looks like the Church is being inconsistent in giving us one and depriving us of the other, since they are so very similar.