I just finished reading the manga and I am not up to date with any statements the author as made
*So most of this is just my interpretation!!!*
Due to the nature of Akito's character, she most likely slept with him out of desperation to prevent him from leaving and to give him another reason to be attached to her. For Akito, her bonds to the zodiacs define her entire existence, it was probably another way to validate that the bond was still real and this may have even been a way for Akito to spite her mom (indirectly). It also probably provided some sort of comfort for her (since we see in later chapters she also sleeps with Shigure after being in an emotionally draining conflict with the other zodiac members). Due to her God complex she believes she has the right to do as she pleases. She also craves for attention and validation so that could be another motive for sleeping with him.
Overall there could have been a number of reasons she slept with him, hell she may have even did it just bc she curious to know what sex was like. Akito's character is complex because of all her past psychological traumas, so truthfully we as readers will never TRUELY understand her thought processes, but we can always assume :) Hope this helps tho!
Thabks a lot! I agree with everything you said haha it simply makes sense.
Can someone explain why Akito slept with Kureno? I know Kureno did it out of pity, but why did Akito?