Assalamu'Alaykum
Habibi - comes from the root word "HABIB" which acually means
"beloved" and Love in arabic is "Hub"
Like brother far7an said,- Habibi is masculine and habibity is feminine.
Ukhtee al habibi is not correct who ever said that must not speak arabic. the correct wording is...
"Ukhtee ya habibity" ( My Sister, Oh my beloved) or "Ukhtee habibity" (My Beloved sister) or i will give benefit of the doubt and assume it was supposed to be "Ukhtee al Habiba" ( My sister, the Beloved)
nothing wrong with a brother saying "habibi" to another brother. and a sister can say "habibity" to another sister.