Sometimes... you really have to ask yourself... no... ask the world a deep and nigh impossible question...
What IS love?
Then... you have to beg it it and your baby not to hurt you.
Joking aside, this is definitely one of my favorite topics to cover here with some of the only people in the world that will get it, so I think you made an awesome choice to come here and air out your issue.
I think what sucks the most, is that none of the advice you get will really feel tailor made, nor are any of us credible experts outside of people who live with similar conditions to you. There's a certain, surprisingly unwarranted, feeling of being an outcast that comes from what feels like an OVERWHELMING attraction to muscle in women. And when you've managed to suppress this attraction for such a long time and build an entire life that treats it as an anomaly or outside force you may not even accept it after you find someone sympathetic or interested in it albiet at a different pace to you. This is especially true when it's their body.
That's certainly been my problem over the years. Meet a girl, get close, tell her what I like, she's cool about it and even flexes or works out for me, and I'm still freaking out thinking I made a mistake. Thinking I could do better. Thinking I didn't explain my situation or my expectations properly. I'm still causing problems after getting the relationship moving in a direction that I want.
So I agree that you should come clean to her as it will help with your peace of mind, but like all solutions, it will invite new problems. Problems that you'll need to be ready for too. Problems like wanting more from her body after she agreed to accept you. Problems like getting over her if she decides to leave you. Problems like, dealing with the fact that she is completely nonchalant about what FEELS like the most important part of your life and sexuality. My god... the people who treat my musclepreciation like regular shit that everyone goes through can actually infuriate me more. I'm not saying their wrong, but all my suffering in my teens means so much less if I suffered over regular ass, everyday problems.
I honestly don't know how therapy will help, but if you get some and it does, please start a blog or something and keep us updated. Because there is very little credible information on our particular crosssection of fetish and lifestyle. And we're all so different - from the types of women we like, to the types of relationships we ultimately want. Do you know what kind of relationship you ultimately want? I've found I don't think about that near enough. What exactly are you looking for? What's your ideal relationship whether its with the woman you're with now or someone else? Do you want her to backtrack on her "muscles are gross" foolishness and grow for you? Do you want to inspire her somehow to grow for herself while you reap the benefits? Do you want carte blanche to do sessions? Or do you just want to venture out into the world and find muscle wherever you can and enjoy it. It's obvious you want to stay together, but you can't as the relationship is now. 5 years is a long time to endure what began in the first month.
I think the best thing we can do for each other here is keep dialogues like this open, and listen and remove judgement from our words to one another as much as possible. We all struggle in our own ways when it comes to being this hard into hard. Larky368 is offering up some tough love, but I don't think his takes are wrong necessarily. All that we seem to agree on is that honesty is better than secrets, love is better than fear, and muscle is important to us. Perhaps the most important thing in our minds. That makes relationships hard, but not because of the muscle, it's because we refuse to acknowledge that importance cause we think we're crazy or broken.
You're not crazy or broken. You're not weird or wrong. Hopefully you can open up and share with your significant other and make that known and have her agree with you. However, even if she does not... it doesn't mean she's right about it. So good luck muscle lust brother.