Please help! (My breast expansion fetish)

Hello, sorry for my bad English. I am searching for help and i hope i could find it here.
My problem is in next: i have a breast expansion fetish. I feel erection when i saw like female breasts are growing. It starts when i had seen film "Pluto Nash" episode in hospital. Since i always looking comics, videos and pictures with growing breasts.
Now I am 18 years old, I have marvelous girlfriend and we love each other. I told he about my problem and se understand it, but she has forbaden me masturbate on growing breasts. She is jealousy and talk that i prefear her to fantsy girls. We have awesome sex but i am still want to watch on growing breasts.
And dont know what to do now. I dont wont to lie, and masturbate when i alone, and i dont know how to win this fetish. Ofteh i am imaginrting her with growing breasts but it help in lettle time.
Thank you very much, i hope you can help me

I know this is old but I have a fetish for growing my breasts with herbs and pumps I love measuring them and staring at them all the time I actually started with a 36inch chest now 43 so it works um if your fetish is growing breasts pay attention to your girlfriends during and after sex breasts swell with arousal.