How can I (M26) open up to my girlfriend (F26) about my porn addiction?

Me and my girlfriend have been together for just about 2 years now, we’ve had a great relationship and I feel like it’s slowly falling apart due to my porn/sex addiction.

To start, I was introduced to porn at an early age, I would say around 8 years old when my neighbor (also 8) introduced me to it. We would watch it all the time together and even try to reenact what was happening in the videos. When we got caught we were in big trouble but that didn’t stop us, we were hooked.

Eventually we moved away and I lost contact, but that didn’t stop me. Everyday after school I’d go in the bathroom for up to an hour just so I can get off to porn. Multiple times a day. I still am doing this now as a 26 year old. Get home from work, watch porn, few hours go by, watch it again. I tried to stop but the most I’ve been able to go has been a few days. I’m not gay but sometimes I’ll even watch gay or trans porn just to see something different, then after I’m wondering why I even watched it.

Where I think it’s affecting the relationship is me objectifying women, and I believe that’s coming from my porn addiction. People I work with, people I see out doing whatever, I just imagine what it would be like to have sex with them. Before I met her, I would have sex with whoever I could, and if I couldn’t find someone out at a bar or whatever, I’d turn to prostitution. Seeing threesomes in porn led me to wanting that in my life, so I’ve had many with prostitutes and even a 6 way once.

I also believe I have a sex addiction to this, whenever I’m with my girlfriend, I am just constantly fully erect trying to have sex with her. She says it’s annoying and it seems like all I want is sex no matter what. I agree with her. I want to talk to a therapist about this to get the help that I need, as it’s been making me super guilty and me pushing boundaries in my relationships. I do not want it to end with me cheating or doing anything I’d regret.

Before I talk to a therapist, I’m looking for advice on how to bring it up to her. I don’t want to hide this from her anymore but I have no idea where to even start with telling her.

TLDR: porn/sex addiction is slowly ruining my relationship. I’m pushing boundaries that I shouldn’t be pushing and need to stop. How can I bring this up to her?