I have to commend you for at least having the desire to do the right thing. I think that's pretty awesome.
I'll admit, I broke up with my boyfriend last week, not only because we were struggling with wanting to keep the law of chastity and were getting too close to messing up, but for other reasons as well. He is an amazing person, but the guilt just got to me too much, and it really hurt our relationship. He's a convert and doesn't struggle with pornography, but struggles with not being sexually active anymore. He blamed himself for all of our problems, but it really does go both ways. Did you listen to that talk by Elder Oaks last conference about desires? They shape who we are. Satan can never tempt you beyond your power to resist. That's something that i've learned throughout all of this. When my desire was to be weak willed and not listen to the spirit that was warning me, I gave in. You sound like you truly want to be with this girl. Then why not make the decision today to change? Go to an addiction group, overcome this thing. And then, don't look back. Alchohol and drug addicts do it all the time, so why can't you? I promise you, that as you take any and all media out of your life, and replace it with good and uplifting things, your thoughts will change. I've noticed it in my life since I got back from my mission. The more movies I watched with sexual content, the more my thoughts gravitated towards that. You may be thinking that's pretty prudish, but maybe you can make a little goal. Like for a month. No Television, movies, or websites with sexual content. Listen to a talk or read the scriptures or a good book during that time. Get out! It's summer. Go hiking or start a hobby with this amazing ex girlfriend. As you take the initiative with your own life, I promise you you'll start to see the changes.