Eli is genderfluid and changes their gender expression every day. What gender they are on the first day is not tied to your pronoun choice but random on the first playthrough and interchanging afterwards.
If fem Eli is there day 1, you will get masc Eli day 2, fem day 3 and so on. And to answer your question: The main character is some variation of pan/bisexual per default, but you're free to headcanon which variation on your playthrough <3
