I am not Catholic, simply a Christian, but I do agree in certain areas about the nature of our eternal security.
One who with all his strength and heart and soul endeavors to please his God and his Messiah is one whose heart is in a position much different from he who loses faith, stops caring, stops trying, and in the end only winds up once more entangled in sin (2 Peter 2:20-21). Deliberate disobedience (not just in a single, sinful act, but in a lifestyle choice) would indicate at least to me a heart that has never known or that has rejected the Spirit.
When listing those who will not inherit the Kingdom, is it not said,
“Cowards, unbelievers, the corrupt, murderers, the immoral, those who practice witchcraft, idol worshipers, and all liars—their fate is in the fiery lake of burning sulfur.”
And perhaps all of us at one point fit in there somewhere! Yet as Paul points out in 1 Cor. 6 (referring specifically to sexual sin), by calling of the name of Yeshua, we were saved, cleansed, and so now we can live new lives. We no longer have to be fearful, incredulous, corrupted, haters or killers, full of immorality, socerers, idolaters, or deceivers–we are free from such things.
Those who live these lifestyles, either before or after receiving the Good News and the very Spirit of God, damn themselves. This at least seems to me to be the case.