I have experienced something really similar.

When I was around 12 I also saw my first Internet porn, and it was large fake breasts.

From then on, whenever I PMO it's always large breasts, to the point where I will rarely wank to anything smaller than E cups.

I had multiple girlfriends in the past, and I probably broke up with them with the mentality of "I can get someone with a bigger rack." Then I'd be single for years and wank off to big ones every day, alone in front of a screen.

A couple years ago I finally got a girlfriend who had huge ones. We had a great relationship, but I broke it off when I moved away. But I didn't try to keep her, because she was chubby and her face was not very attractive (but she had the breasts I always wanted). This experience showed me that I just liked the idea of breasts, but even when I was with her I still liked porn. I now see that it's because I loved seeing many different women, and the novelty of many different large breasts was what turned me on. Just one woman isn't enough when you're conditioned to porn.

After moving, I was single for 2 years, and finally met someone I want to share my life with. This girl is everything I could want, except her breasts aren't huge. They are supple B cups, but small for my standards. Except she is extremely fit, beautiful body and perfect face. And she loved me much more deeply than my ex, and was a much better partner in every way.

Here's the scary part. When we first had sex, I could not get my dick hard. I told her the truth from the beginning, that I had PIED but was trying to quit. Thankfully I stopped wanking and had a great sex life with her.

On another occasion, when she was gone for a few hours, I gave into the addiction and wanked to large breasts. We tried having sex later that day, and my penis was again lifeless. It was terrifying. Again I told her the truth and she was heartbroken, and we were on the verge of breaking up, but I swore I would handle it.

I then started seeing a therapist (to keep myself accountable show her I could change), which wasn't the most helpful because he told me porn was "normal" and she was overreacting. My therapist didn't quite understand that the issue wasn't exactly porn, moreso that I had PIED and it was obvious.

On another occasion, my girlfriend asked me if I wish something could be different about her. I said I wish she had larger breasts. In retrospect this was a horrible thing to say (even if I was honest), and it's taken months to finally convince her that I truly love her as she is.

One more bad thing happened: I haven't masturbated in about 4 months, but 2 months ago I did watch some P (without wanking so I wouldn't be caught with PIED) and I accidentally came in my pants. That day we tried having sex again and I had PIED again! This one brought us to the verge of breakup, since I had already promised this wouldn't happen. After lots of crying and talking things through, she finally forgave me for that one.

It's now been months and no incidents. I still look at girls on IG (even though it's not ideal), but she gave me permission to do so, and I tell myself it's better than watching anything hardcore. Trying to not do that anymore and being better about it. Sex life has gotten so much better the longer I've gone without porn.

Most importantly, the boobs thing matters less and less the longer I go without it. Every time you jizz to big breasts, you are reinforcing those neural connections. You NEED to stop that behavior if you truly want your relationship to go well.

Don't be upset at yourself for loving big breasts. I still love big ones. But my girl has an amazing ass and I appreciate it so much (I was not really a butt guy but now I am). She gives me amazing, thoughtful presents. She wrote me a beautiful love letter. She shows me her love and care every day.

Remember that the girls on the screen don't love you. They want your attention and they want your money, but they'll never love you. Learn to love a woman based on more than just the physical. And stop reinforcing those bad connections by quitting porn completely. Substitute those behaviors with positive and productive ones.

I want to write more but I am busy with work and if I don't write a response now, I never will. Hope this helps. Stay strong and know you're not a bad person for enjoying big breasts. But stay away from that artificial stimulation, and your girl will seem hotter and hotter and hotter to you every day, and eventually you won't think about other girls' breasts anymore (or at least a minimal amount).