And that even though she can tell, just from looking at a picture, that the new girlfriend is trans, so therefore clearly doesn't pass, she still thinks the new girlfriend is a "better" woman than she is.
And she's right.
Under patriarchy, men see women as inherently flawed. Gender, i.e. femininity is the cheese men put on the woman-bread before they eat it (cannot remember where I read that but it's a great metaphor).
To expand on the metaphor, like a spoiled child, they'd rather have the cheese without the bread.
So, male+femininity = better woman.
Unless he wants children, but in that case, the transperson's sister can be bullied into risking her health to give him babies. Or, if there is no sister, a woman from a third world country can be exploited for that.
We have reached the stage where men can outsource the babymaking to people they don't have to live with. And I think many misogynist guys like that option very, very much.
I don't think it's a loss - if he prefers a femininity performing male to her, then he never was attracted to her as a (female) person, just to femininity. It's a rather common phenomenon, just think of all the men who hate women but are still in a relationship with one. (Or perhaps they just love the idea of being heterosexual? Then, too, a transsexual will make them happier.)