For those who are plagued with an addiction to something mortally sinful, below is a link that should give you hope. You may not be as bad off as you think you are . . .
Father Angel addresses whether someone who is trying to overcome an addiction has the “complete and deliberate consent” necessary to be guilty of a mortal sin. In a nutshell, my understanding from what Father Angel says is that mortal sin cannot be present for someone who sincerely desires to overcome an addiction through prayer/fasting, even if it is an addiction to something gravely sinful. He says, “The pious, heartfelt, and religious affectation/desire to please God is not compatible with the intentionality involved in mortal sin.”
I would go on further to say that for one struggling with such an addiction . . . any doubt as to whether one has completely consented to the thought or act is a certain sign that one has not given his “complete and deliberate consent.” In addition, like Father Angel says, mortal sin involves someone who does not care about offending God. So, supposing one falls into temptation and dwells on a thought or performs an act which would otherwise be gravely sinful, one’s upset, distress, or disappointment after the fact is a sure sign that one does care about offending God. It matters not that the thought or act was enticing and/or enjoyable during the experience . . .
The remedy to overcome this struggle is frequent confession, Holy Communion, and acts of charity. Note that because one in these circumstances is not guilty of a mortal sin, that person should receive the Eucharist, even BEFORE he has had a chance to go to confession.
This makes sense . . . the Eucharist is the healing remedy. So, in order to be healed, one must receive the Eucharist. And, the more frequently one falls, the more frequently one should receive.
Our God is more merciful than He is just and He is on our side. Do not let doubts presented by the enemy of our souls keep you away from the One who heals.
May God bless you all.