"Can I ever be forgiven"? You often ask. Yes, you can because for our God impossible is nothing.
Replace previous question with "can I do any good for others" and trust. And if temptation to commit the greatest sin of all, that is to despair, somehow prevails, think of Saint Peter, Saint Thomas, Saint Paul, Saint Augustin, Saint I. Loyola, Blessed Bartolo Longo...
These "sinners" lived for us... As the visible signs of God's infinite mercy.