I am a man who after going through the work in rebuilding my masculinity, realized I was a pansexual person. Part of the work utilized understanding my desire for a strong feminine spirit in a human being.
That led to spending time looking and understanding transgendered women. I like your partner find them highly attractive also (just like I find biological women too).
Now women are women, and as I unpacked my needs in a partner I started to understand what my missing needs were.
As for you, it is totally understandable how a biological female could feel threatened by a woman with extra features or abilities that she doesn't have.
Luckily we live in a wonderful time where there are toys and things that women can use to simulate those parts.
So when alone and being intimate you can look at things like feeldoe's and squirting dildos and enhance your sexuality and try new things out since your partner is very open to it. Imagine the two of you going to bed and you waking up before him and sliding on something and waking him from his sleep with a little surprise just like women have done to them many times.
Given patriarchal training and in today's light women definitely have a large divide to conquer with confidence. But men also have just as large of divide too, and given men have lacked the audience and ability to jump and have partners and friends to talk to ... he literally did this alone.
Luckily it was you he met up with so he could be whole. He could be in my position which is another whole hell.