Comparison is the thief of happiness. For cock size, doubly so.
I wanted to try to address this in a way that's constructive to your situation... by way of reframing comparisons.
Sure, it's a big confidence boost to men to be objectified like that over other men, but that's called "downward comparison" and is done at the expense of others. In this case, it's unearned. You're born with the bone you got. You sound like you have a perfectly average cock and are objectively larger than a lot of guys already. Take pride in that. But if you are obsessed with wishing you were an outlier on the higher end, instead of "stuck" in the middle with all those other cocks, that worry is going to sap your confidence. You can't change your penis size, so put down the tape measure and close the browser tabs full of lies about enlargement. Women can smell penis envy on a guy from a mile away and it's a pretty universal turn-off.
My advice... own and master yourself. Meditate on your thoughts, feel the insecurity, take a deep breath, and then let the thought pass like a floating cloud. Keep breathing from there with a clear mind, and your body will learn to let the insecurities and the anxiety go. This is great for all manner of jealous thoughts, but it takes practice. Took me almost 8 months to master this in my situation.
You are perfect the way you are. Develop your confidence. You sound like you have a nice Hephaestus-vibe going on, despite your insecurities. Lean into that.
Consider that your partner is keeping you around despite the cocks she has to pick from. You clearly give her something she doesn't get elsewhere. Maybe that's sensitivity, loyalty, and security. So what if you don't have a monster dong? This is just another side of the "can't be everything to everyone". Neither can the hung guys. In the non-mono world, if you're in her life, you're here because she WANTS you here. Take comfort in that.
Consider that the size queens simply aren't all they're cracked up to be. Even a 7.5-8 incher is going to feel inadequate when a queen's eyes start looking for bigger. And if you're honest about what you are with a hookup and she blocks you on 4th Down and Inches... SHE doesn't deserve what YOU have to offer. So, bone up on your self-respect and be prepared to let those kind of women go, perhaps with more poise and grace than they afforded you. Be the "bigger man", ironically if necessary. And it's not all great for the owners of big cocks either. Sure, they get more attention... and sky-high expectations. If men think a bigger cock will solve all their problems, what about the women who think a guy with a bigger cock will solve all their problems, too? How many women might be looking for an average cock for their next partner after a bad experience with the self-absorbed owner of a leviathan? (This is a poly forum after all, and there's more to a good relationship than sex.)
If you're looking for more female attention... level up your oral game. There's a well-known "orgasm gap" between the sexes, and women aren't getting enough. Most women do not come from PIV intercourse. Across my five partners, I've only seen it in two. That jives with most statistics on the matter, even trending toward me being a little lucky to have seen it more frequently. (Oh, and in terms of "luck", I'm packing about as much as you are.) Focusing on your oral technique can add "inches" to your "total package". I recommend Ian Kerner's "
She Comes First". He wrote that after feeling crippling shame at his premature ejaculation and ended up penning what's one of the best treatises on the subject.
Furthermore, cultivate your gratitude. Be grateful for the good things in your life instead of thinking about the things you don't have. Think about what fills your heart, hold that thought in mind... and then SMILE at the thought and fill your heart with the warm light of gratitude. That can be the basis of your self-confidence, which will turn around into attractive outward confidence.
And finally... if you want to have a bigger cock... have someone else's bigger cock. I'm serious. You seem like you're already leaning in that direction, though you have trouble finding a good match. When you do find a nice big cock attached to a partner, appreciate it, be happy its owner has something special (compersion anyone?), and appreciate its owner is sharing it with you. I remember seeing a guy with a real monster at the club last time we went. I mean, geez... that poor woman looked uncomfortable. I also remember feeling a little flustered myself, thinking it would be nice to play with. I was just happy to know he had that extra blessing. (I also suspect he was a professional the club owners called in to add some extra action to the open bed area. See, even this has the potential for perception distortion.)