Catholics should worry most that they don't act against the virtues of purity, modesty and chastity
Indeed.
If you had to pick one weakness or sin that you want to be strong against, always pick chastity/purity.
All other sins are easy to conquer compared to the demon of lust.
I'll never forget this chapter I read in a TAN book called "The Sinner's return to God" with a picture of the Prodigal Son on the front cover. It was the chapter on impurity.
A man was on his deathbed, and he had renounced all his other sins, EXCEPT he was living in sin. He had a mistress.
The man was otherwise disposed to make restitution and separate himself from all his other sins, but despite the priest's pleading, he wouldn't send away his mistress.In the end, he embraced her and said, "I could never renounce you" and died while in the act of embracing his mistress. Thus, the miserable wretch almost certainly went to hell.
What a horrible hold sins of impurity have on a person. And remember Our Lady of Fatima said that sins of the flesh are what the majority of hell's inmates were guilty of.