It's an interesting question. There is no hard-fast answer, but there is an implicit suggestion in the way that D&D 5e has adapted to a more updated view on diversity.
So, in your quote about Kiltzi it mentions that the "favored form of devotion" is between a man and a woman. This in itself does not mean that it is exclusive. You could have you character be many times devoted as others for instance. The devotion practice itself is not specific. It could be sharing intimacy on many different levels, not just sexual intimacy. Also, consider that Kiltzi possibly has another facet, which could be hidden to the world at large, but which your character is in touch with. Maybe it is part of your character's purpose to enlighten Kiltzi's followers and show them that she favors all forms of love devotion.
Discuss this with your DM: if the script doesn't fit, just ask her/him/them to change it.
Remember, the information about Kiltzi was published almost 30 years ago (Maztica Campaign Set, 1991) and D&D (and society) has mostly come a long way since then. I played the first edition D&D and AD&D so I'm keenly aware of this. For instance in the PHB (p. 8) of AD&D there is a whole self-justified blurb about this:
A Note About Pronouns: The male pronouns (he, him, his) is used
exclusively throughout the second edition of AD&D game rules. We hope
this won't be construed by anyone to be an attempt to exclude females
from the game or imply their exclusion. Centuries of use have neutered
the male pronoun. In written material it is clear, concise, and
familiar. Nothing else is.
[Thank the Gods that is not in D&D 5e.]
There has been, and quite rightly so, positive changes in D&D 5e so that it is more reflective of and embraces a wider variety of narratives. You can choose your character's sex, gender, sexual orientation - and it actually says so in the 5e PHB. The materials are widely gender-neutral now too and say "he or she" - which is great because we have a lot of women players. Implicit in this too, is that the DM can also adapt, update or create deities and pantheons which suit the campaign and the players'/characters' preferences. The main thing is that you and your group enjoy role-playing your characters and their adventures.
The section in Chapter 4: Personality and Background of the Player's Handbook/Basic Rules relating to your character's sex supports this wider view (PHB, p. 121):
You can play a male or female character without gaining any special
benefits or hindrances. Think about how your character does or does not
conform to the broader culture's expectations of sex, gender, and
sexual behavior. For example, a male drow cleric defies the
traditional gender divisions of drow society, which could be a reason
for your character to leave that society and come to the surface.
You don't need to be confined to binary notions of sex and gender. The elf
god Corellon Larethian is often seen as androgynous, for example, and
some elves in the multiverse are made in Corellon's image. You could
also play a female character who presents herself as a man, a man who
feels trapped in a female body, or a bearded female dwarf who hates
being mistaken for a male. Likewise, your character's sexual
orientation is for you to decide.
May the many hues of Corellon's light shine on you!