I am no expert in these things, but my wife has wondered whether my desire to crossdress is because she isn’t included to sexy lingerie, nice nails etc. Alternatively, it may be they are trying to ‘enjoy being girls together’.
That said your partner is extremely lucky you allow them to dress as they like and you are even prepared to go to a trans night with them, very few partners are that accommodating. At the the risk of being controversial it seems to me you allow him/her to wear whatever she they like, even presenting as a women, and they should allow you to present as you wish. So if, for you, dressing in a less girly manor than your partner does that should be fine and they should not try to change it, just as you aren’t trying to change them.
I think you should gently tell them this before it becomes an issue and impacts their dressing. Good luck.