I find myself conflicting that I try to be a good Catholic/Christian--I participate in mass every Sunday--yet I am a slave to sin and such sexual fantasies. I feel like I'm only doing the bare minimum to serve God--I don't pray to Him before eating or bed, I only pray when I am in need of something. I haven't gone to confession in over two years but I feel like I should go. God knows our hearts, and I feel like my heart isn't in the right place.
We are all slaves to sin, for that's how we are as humans, and that's why God gave us the New Covenant to ultimately redeem us of our sins through His blood sacrifice as our high priest in heaven, to fulfill His justice and redeem us of our horrible, inherited (and therefore natural to our minds, for this evil has been passed down to us from as far as the first fallen) aggression to His will. You are a sinner as am I, and there is no distinction, for we are one in Christ. The issue you suffer is that you shouldn't live
in it; you should be actively trying to climb
out of whatever holes you stumble into. You're stuck in a trench of sexual immorality, very clearly, so you need to climb out of it. You aren't on your own in such a struggle, because, by believing in Christ's redemption of us, by tightening our faith firmly around us, by convicting ourselves to all of what He has commanded, by striking down our sins off of their pedestals, and cleansing the temples, our bodies that the Holy Spirit inhabits, through putting instead on these pedestals the word of God, for it to ring and echo in us (for the Gospel has been shouted in our hearts to forever bounce from all walls of our souls), by doing this, by going on the faintest impulse of God's will instead of the strongest thoughts of your lust, by clicking off the tabs you have of the wretched flesh and turning the pages of scripture, you will not be alone in such a struggle, for God is within your own heart, and He is there to talk to, right now, as you read this, so do so. Speak to Him, and feel that connection with Him, so that your heart may feel the guilt of your past actions as fully as God desires it to, and your soul may re-attach to the guidance of the Holy Spirit through such an intimate, caring talk that He lets you have with Him. Do not take such a thing for granted, for God has given us all a privilege in speaking directly to Him, and it is a great blessing.