Porn/Masturbation addiction

Hey everyone, this is my first post on here and I just wanted some advice and support about this.

I've been with my girlfriend for 3 years now and I love her more than anything in the world. She's the first and only girl I've ever had sex with and she always wants to have intercourse with me, but for some reason I kept turning to porn and masturbation.

I hate that I've been doing this and I've been clean for a while now but I want some advice on trying to keep it that way because it's ruining my relationship with the woman that I love.

Thank you.