There’s a great article I would
recommend you read.
One of the great principles you’ll find therein is this one:
If you are not certain about your consent, you did not consent.
The article gives numerous examples of this principle, my favorite being the one about a man asking a woman to marry him. Does she know whether or not she said yes? Does she wonder about it? Of course not: she has no doubt about whether or not she consented.
… and THAT is the sort of consent of the will we have to have in order for us to commit a sin with our thoughts.
Moreover: Grave matter + full knowledge + PARTIAL consent = venial sin.
If you’re in some way resisting temptations, especially dealing with the sixth and ninth commandments, then you’re at most giving partial consent to them, all other things being equal.
Now, someone mentioned pure thought not being a big deal. This is true, so long as our will doesn’t consent to those thoughts! The entire ninth commandment, after all, deals with sins of the thought.
Finally, from the article, here’s a great commentary on this entire situation of having impure thoughts go through one’s mind, and whether or not one has sinned during that process:
“Now comes the question of temptation to mortal sin. Let’s say that an indecent but attractive picture flashes through a man’s mind. Later, when he recalls having had that thought, he asks himself whether or not he consented to it.
“It is the clearest thing in the world; if he consented, he knows that he did, and that is all there is to it. Or let’s say that he fought it away and vigorously said no; then he knows for a certain that he did not consent to it.
But if he remembered only that he was very confused and muddled and excited at the thought, that he liked the temptation and yet knew it was a sin, that he wanted to accept it and yet felt that he must not do so, that in the end his mind was spinning around in circles, what then?
“The answer is very clear-cut: If he is absolutely sure that he was not absolutely sure, then he was not sure at all. And if he was not sure whether or not he consented, then he didn‟t consent.
“And the person with scruples just has to say, „If I am not absolutely sure whether or not I consented, I did not consent.‟”