Here’s a long winded post for ya, as I have found some time on my hands:
Hehe, I do not really know the answers myself my brother, lust is an elusive beast. I think using your honest judgment guided by holy teaching, a confessor, and grace will yield you the best answer, and over time you will develop a better sense of when there is and isn’t lust. Just remember:
-the Church teaches that mortal sin requires BOTH full consent and full knowledge (what that means is not entirely clear, and I think that is for the best), while being of a grave matter.
-as far as what constitutes the grave matter of lust, I myself am unclear on it. In my own experience the best label I can put on it is one of describing my experience. Lust seems the realization of impurity of heart in regards to physical beauty (which is a great thing IF removed from the impurity). The only other way I can identify it is by its effects. When I am expreiencing a temptation of lust or even the indulgence in it in sin, it seems my mind is narrowed to where I can no longer HONESTLY love the object of my lust. That is, it seems incompatable with maintaining the will of goodness for them and others in all things. Hopefully that is of a bit of help, though you must remember I am speeking with no authority on the matter, and my indicating what it is might be too narrow or too wide.
-venial sin is not REQUIRED to be confessed, only mortal sin
-Also remember that no mere experience of temptation makes you guilty (but it is a good reminder of your fallen state). Insofar as you are a healthy man, you are going to find your thoughts and impulses wandering and so forth, all you must do is make sure your will (that is YOU pure and simple, not your appetites, not your inclinations, but YOU) isn’t wandering. When you find yourself in such thoughts, the second you are aware and have a choice to make, make it. Choice (the object of the will) is where sin lies (or lack thereof), not in the impulses and habitual or natural movements of the eyes (that is not to say you do not have a separate duty of destroying such habits by habituation insofar as you are capable).
That is my advice on lust anyhow. HOPEFULLY it is sound

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As for scrupulosity…
It appears to me that you are dealing with scrupulosity.
However, I think that is something more for you God and your confessor to determine over a good period of time.
In my own experience scrupulosity is overcome over time (I speak as one who is entirely over it, which is not entirely true

) with experience and with the realization of the devil’s ability to paralyze the scrupulous with paralyzing legalism after you turn yourself over to wanting to please God in all things. You see, if you are not easily prevented from confession, the most logical thing for the devil to do is to make confession itself a stumbling block. One who suffers it, in my opinion, will probably eventually realize that the paralyzing legalism is not necessary for giving yourself over to righteousness/God (note: I speak of PARALYZING legalism. We ought to obey all doctrine 100%, but not get too caught up in the particulars for every moment holy duty calls even in the most simple things. If we get hung up on the particulars we neglect our present duties I think)
On a further note, 99% of all my troubles with it were on matters of lust and on matters of brief (for the most part unwilled) thoughts or past sins I would be most embarrassed to confess. Hitting the golden mean is hard, and since the devil also tempts us (in the opposite way) to keep things from confession, due to the embarrassing nature of them,
I think only good experience will teach the scrupulous what they ought to confess and what they ought not (to avoid being paralyzed).
Realize that this is a cross, and then your suffering in it can find meaning in following Christ’s footsteps. It is often said that the holy mean lies between two unequal excesses/deficiencies. One is worse than the other. For example, hedonism is much worse than the rejection of all pleasures as evil, though both are evils. If you and your confessor determine you are scrupulous at least take joy that you are perhaps moving onto the least of the two evils (scrupulosity vs. uncaring). PERHAPS bending the wood beyond the place you need it to rest at is a necessary step.
And perhaps more effectively than all this long-windedness, I shall say a prayer for you brother

. May St. Padre Pio intercede for you on matters of fruitful confessions, may St. Michael intercede for you in your struggles to gain self-mastery in all things, and may St. Anselm intercede for you in matters of clear and proper logical reasoning.