And the action itself (c) could be the lingering on lustful or impure thoughts and doing nothing to stop them, and thus a sin. Just because you didn’t want to be tempted doesn’t mean it’s not a sin if you succumb to the temptation and linger on them. The “action itself” doesn’t have to be physical.
See Matthew 5:27-28: "You have heard that it was said, ‘You shall not commit adultery.’
But I say to you, everyone who looks at a woman with lust has already committed adultery with her in his heart.
My concern would be getting into the habit of blowing it off because you didn’t think you had any control, even if you really did. I would liken it to picking a fight if you were drunk. It’s still a sin even though you were drunk and not as in control as if you were sober.
I would also suggest reading the following articles from the Catechism of the Catholic Church:
The Battle For Purity (specifically 2520 and 2523), and
The Morality of the Passions (this is the start page for the article which ecompasses paragraphs 1762-1775 – you have to click the “next” link a few times to read the entire article).