Feeling sorry for hurting someone you love is a natural result of human emotion. You must realize:
*]what you’ve done
*]that you’ve hurt him
*]how/why you’ve hurt him.
Thus, in the case of sin, you must know and clearly understand the sin – then the gravity of the situation will sink in. Many masturbate, contracept and murder their unborn children and do not feel remorse, because they do not understand what they’ve done.
I therefore recommend reading more about the sins and what they’ve damaged. In my case, I’m currently reading Theology of the Body for Beginners by Christopher West, already having read his Good News about Sex and Marriage, and understanding why sins are bad and what God’s plan is helps me immensely in avoiding evil. It’s like any math or physics problem – you can’t solve a problem if you don’t understand its solution.
If you already have a mastery regarding knowledge of the sin in question, then I would recommend praying, going to Mass and Confession more often, etc. – essentially, try to grow in your spiritual life. Monday, I told a priest that I might have my priorities mixed up, occasionally placing my schoolwork before reading the Bible and “spending time with God”, etc. – the priest gave me great advice concerning my spiritual life: Don’t try to compartmentalize God, praying before a meal, and then eating the meal forgetting about God; as a college student, praying before a test, then forgetting about God while taking the test. Rather, everything you do, do it for the glory of God, for the will of God. Taking the test, going to work, do everything for the glory of God – in this manner the Holy Spirit lives within us. (I don’t mean that we should try to think about God every waking moment of our lives, but rather realize that God is everywhere and do everything to please him.)
A woman once told me about how her guardian angel followed her everywhere, thus she tried to always do things and go places where he’d be comfortable. It’s the same idea.
I hope this helps.