I have a friend who watches porn. Ironically, she did not get addicted to those images, but I did. I prayed and asked God to cleanse and to forgive me. It worked for a couple of days, but each time when I meet my boyfriend, I got reminded of those images and start to forget all about the Bible. I did oral sex and dry humping on him. He's not a Christian. He cannot stop the temptations to touch me, and I yield to it. I regret it after each episode, even though I was willing. Please tell me what to do.
"For godly sorrow produces repentance leading to salvation, not to be regretted; but the sorrow of the world produces death. For observe this very thing, that you sorrowed in a godly manner: What diligence it produced in you, what clearing of yourselves, what indignation, what fear, what vehement desire, what zeal, what vindication! In all things you proved yourselves to be clear in this matter" (II Corinthians 7:10-11).
What you are saying is that you have sorrow without repentance. Repentance is a change of heart regarding the wrong you've done that is accompanied by a change in behavior. You regret what you are doing, but you make no changes.
It appears to me that the cause is your passive approach to morality.
Let's start with your friend. She watches porn. Since she continues to do it, regardless of her claim, her actions say that she is caught up in this sin. You saw pornography and you can't seem to get the images out of your head. Unfortunately that is the design of pornography. They provide shocking images that are hard to forget to tempt people to come back and see more. Just because your remember the images, it doesn't mean you are addicted. It only means you have a good memory, even when you would rather forget. But notice that you let your friend dictate what you watched. You didn't walk out. You stayed and watched.
You prayed for help, asking God to remove the thoughts. Notice that again you wanted someone else to make you good. You want to be good without the responsibility of having to say "No" to sin. This isn't how you avoid sin. "Be sober, be vigilant; because your adversary the devil walks about like a roaring lion, seeking whom he may devour. Resist him, steadfast in the faith, knowing that the same sufferings are experienced by your brotherhood in the world" (I Peter 5:8-9). You gave little personal resistance.
Then when you saw your boyfriend you blame those images as the reason why you imitated them. The images gave you ideas of what you could do to your boyfriend, but they didn't make you do anything. You chose to sin.
In addition, you blame giving in to your boyfriend because he touched you inappropriately. You excuse his disrespectful behavior on the fact that he isn't a Christian. All that tells me is that he might be ignorant of proper behavior, but that doesn't mean you are ignorant. "Now concerning the things of which you wrote to me: It is good for a man not to touch a woman" (I Corinthians 7:1). You could say "no." You could walk out, but you again passively choose to sin because it is offered and you like it.
Given the situation, eventually your boyfriend is going to bored of the same old dry humping and oral sex. He's shortly going to want full intercourse. When it hits, you two are going to so caught up in sexual passion that after he finishes ejaculating in you, you'll both wonder what happened. But what happens is as predictable as the sun rising in the morning. You don't say "no" so you keep playing with sexual fire. "Can a man take fire to his bosom, and his clothes not be burned? Can one walk on hot coals, and his feet not be seared?" (Proverbs 6:27-28). Being nice and cuddly with a flame doesn't mean it won't burn you. It is the nature of fire to burn. Just because you didn't intend to walk on a hot coal; it doesn't mean the coal will say, "Oh, that was an accident. I'll ignore you." The nature of hot coals is to burn. Your intentions have nothing to do with the matter. The same goes for sex. It doesn't matter that you are just trying to be nice or that you have no intentions of getting pregnant. The nature of sex is a drive almost beyond reason for the man to have his penis in the woman's vagina and to ejaculate semen there. And that is where this relationship is heading.
Already sex dominates your getting together. It is no longer about getting to know each other as persons.
Even before he manages to get his penis into you, you have been running risks of getting pregnant. Sperm is present in his semen and sperm swim. If semen gets close to your vagina in any manner, sperm can swim up the vagina and into your uterus. The odds of survival are very low, but they are not zero. If you do become pregnant, you can't claim that it wasn't your intention. Sperm don't ask.
God is not going to make you be good. You have to want to be good. If your boyfriend can't keep his hands off you, then you need to find a better behaved boyfriend. You need a man who respects you, not a boy trying to corrupt you.
What then, can I do to repent thoroughly and have God forgive me?
You are going have to make up your mind to live by God's standards. "Jesus answered and said to him, "If anyone loves Me, he will keep My word; and My Father will love him, and We will come to him and make Our home with him. He who does not love Me does not keep My words; and the word which you hear is not Mine but the Father's who sent Me"" (John 14:23-24). It is decision in your mind and the way that you behave. No one makes you do right, it has to be your decision.
I don't know whether you actually became a Christian, or just call yourself one, but read How to Become a Christian. If you are a Christian in truth, then you need to talk to God about your sins. "If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness" (I John 1:9).
You can't keep hanging around people who push you to sin. "Do not be deceived: "Evil company corrupts good habits"" (I Corinthians 15:33). Sin is hard enough to battle without "friends" encouraging you to sin. Find good friends among good people.