Terrified

My recommendation is to find a therapist who can help guide your disclosure to her, because the disclosure process itself will have a major impact on her healing process. I think it's great that you are trying to quit and even greater that you recognize the importance of communication and intimacy and honesty with her. It's a process you have to be brave through because it's risky and scary, but it's also necessary to restore the relationship because withholding the information is dehumanizing and devaluing her.
Start a journal. When you want to talk to her and can't bring yourself to, wrote the thoughts down so that when you and her are finally communicating about it, you have what all of those thoughts were to share with her IF she would like to have them. Find the therapist, preferably a CSAT. Organize a full disclosure. Tell her as soon as reasonably possible.
My husband and I are not going to work out even though he got clean immediately and has been clean ever since he got caught. Biggest reason is because he did not come to me on his own. He had to get caught. Second reason is that I never got a full disclosure. He waited long enough that he could say he "doesn't remember" to most of the things I wanted to talk about as part of the disclosure. He drip fed information that I pulled out of him like pulling teeth until it stomped out my ability to heal with him and trust him. I didn't feel valued or like he had any care for me as a person at all. The disclosure is important.
Doug Weiss will likely be really helpful to you at this point in the process. I don't agree with everything he said, but he was probably the only resource that really made my husband see what recovery and not just sobriety looked like and to see what communication was supposed to be.
Please get clean ASAP. I know it's hard. But think about it in reverse, if SHE were looking up other mens' bodies to get aroused to every time she got stressed. What if SHE were looking up perfect male bodies to masturbate to? Bodies that likely didn't look anything like yours, that preyed on your insecurities. What if she focused in and stared at features you could likely never get when she wanted to get off? Immerse yourself in the feelings you would feel around that and then realized that she grew up in a society that was already telling her she wasn't physically good enough and never would be.

 

Practically speaking, you need to identify your triggers and the compulsion process. Stress causes you to relapse. So when you start to feel stressed, what steps are you taking to build other coping skills? What steps are you taking to avoid other parts of the process? (Do you always go to the same spot? Do you always use your phone? Do you always organize the experience in the same way? And then in what practical ways can you interrupt that?) My husband always went to the bathroom to do it, so his practical step was to just never take his phone into the bathroom, regardless of whether he felt like he was in the addiction funnel or not. It's just his new normal that the phone does not go to the bathroom. He has not relapsed once (I have a shit ton of home brewed monitoring software on all of his devices and our router that he does not know about because I used to work in this field professionally) because that interrupted the compulsion and habituated process surrounding his use.

 

If you tell her, she's going to flip out.
But my biggest concern is that you can't stop. What are you going to do differently to help achieve a better result?
If nothing changes, nothing changes.

Seeing a CSAT and a support group would be a great start. But would you be able to keep these things secret from her until you're ready for disclosure? I, myself, would be okay with it. Relapse is common in early recovery. But you've been on NoFap since 2016 which makes you a chronic relapser. Once disclosure is done, these relapses will only tear your wife apart more.

I am not convinced that every wife wants to hear the truth. I know of many wives that would prefer to stay in their blue bubble. Many members on this forum disagree with my stance. They believe that complete honesty and disclosure is always the best policy. But I know that this type of honesty carries a high price. I know where it often leads to. So I'm not going to quickly encourage someone to voluntarily march in front of the firing squad.

My main reiterating concern still remains. How are you going to stop? If you can't stop, it doesn't matter how honest you are. Your behavior will ultimately destroy you, her, and the relationship.