Karen, first I want to say that not being allowed to dress / present for sex the way I want to would be intolerable. If that's what you needed to be aroused enough for both of you on have the pleasure of intercourse then asking you to do otherwise is honestly cruel in addition to effectively sandbagging mutual pleasure. I'm no saying she intends that ... it's clear she doesn't understand.
Viagra is unlikely to help, it's effect depends on the presence of arousal and if that's absent, it will only give you the side effects.
I remember all to well, right around the time I told my GF I needed to transition one time in bed when I was just feeling awful, knowing she was not wanting me to transition. I was on the verge of tears and while I was still keeping it up I had to fake orgasm to end it before I was going to lose my erection and have to explain why 😥. I promised myself right then I would not put myself in that position again.
I was in a nominally more open situation than the OP, I'd started presenting femme for sex shortly before I met my GF and in 17 years had never presented otherwise so really, she ought to think transition was on the table.
Also for the decade prior I shifted to basically never reaching orgasm during penetration and eventually often not wanting orgasm at all, only to press myself closer than close, to feel intimacy. It's not that I ever didn't like my libido, I just have a very different feeling about it now.
And all this progressed before I started HRT. My body and mind had been forcing them issue. Of course I'm now a year post op and her actually made me more jprny, just l3ss obsessive about it. I fear I may be at the Rubicon again, in fact right around the Ides of March I really began to feel my ambivalence in sex with someone who continues to gender me as male. We've made it a long time and I'm not giving up on it yet, yet I'm finding I want to be with someone who can give me pleasure he same way I do her.
I do hope we get there and I also need to allow for the possibility that we both may be better off in different primary relationships.