Fair question
I'm used to maintaining an outwardly masculine persona, I've done this ever since my boobs first started growing when I was a teenager. So this is also what I acted like when we first met.
Looking back, she did try to "test" me several times at start, she used to wonder how I'd look in her lingerie or how I'd look with makeup or lipstick on. Being a tough guy like I am, I just laughed it off.
But in reality even these pretty mild comments used to send me into deep shame, crossdressing and gender dysphoria spirals. Growing up with boobs as a dude tends to give you a hair trigger about this I guess.
She probably picked up on some vibes related to it, stopped paying attention to them and my breasts basically became a taboo topic in our relationship for a while. She only commented on them or touched them when she was pissed off at me, because she knew I'd get weird about it.
A few years ago, things started somehow thawing again though. When talking about each other's favourite attributes, she said that she thinks my best assets are my breasts and butt. Sadly, when I suggested that it should be my dick instead, she just laughed and shook her head.
She also now sometimes asks me to wear tight tshirts, because they "bring out my curves". She also very occasionally grabs my breasts when we have sex. It has always made me finish pretty much instantly, which is super embarassing.
But some essential barrier about this is still unbroken. I guess neither of us are willing to break a familiar and working pattern because we're still not sure how the other person would react and where it would lead. I don't even know myself, outside I am a straight man but on the inside I'm a bisexual sissy who enjoys having big bouncing tits on her chest. Should I let her out or not?
The masculine role is useful, familiar and its what she likes in bed, and in a man. The occasional flashes of femininity are allowed, but wearing a bra? It's a huge step up and a pretty clear signal towards embracing femininity.
I'm sure we both have our theories and know more than we let show, but how much? Is it tolerated as long as it's covert? Does she actually want it to be more overt? How many layers of Yomi are there between us?
Maybe I'll find out eventually.