(Instead we had Yoimiya who isn't even from Sumeru and she's his main girl in that region)
At first, every Sumeru Males want Nilou as their wife because of her beauty, her art appreciation, so, she's the first one likely to be taken. Cyno won taking her first. So, the others had to search for alternatives. Kaveh finally finds Faruzan and takes her. Meanwhile, Sethos takes Collei, as both are the same age and are Tighnari and Cyno's apprentices.
At first, Wanderer, Alhaitham and Tighnari can't decide who to take. But some time later, the Traveler Twins arrive at Sumeru. (The Traveler finally recovers their sibling and they both search for their respective suitors in Sumeru). Wanderer sees in Lumine a de facto suitor (Beautiful as Nilou) and takes her. Aether, in other part, can't decide between the remaining girls: Layla, Dehya or Candace. The same happens with Tighnari and Alhaitham. Who would you pair the remaining ones?
- Aether x Noelle - They fit better in the Lunar Crystallize team. Geo Aether's Burst provides 10% CRIT Rate, while his Geo creation can shake the ground with Zhongli's skill. Noelle is the DPS with her Burst. Bina provides them an ability to make Lunar Crystallize.
- Aether x Hu Tao - Together, their best synergy is with a Overload team with Chevreuse. Beidou also helps with her Sub DPS burst to aid Electro Aether while Hu Tao is the main DPS.
- Aether x Ayaka - The best they can is a Freeze team with Venti grouping enemies to allow Ayaka's burst hit all of them. Hydro Aether can hit them in this state with his Skill pressed for long. Sigewinne is their sustain
- Aether x Dehya - They thrill better together in a Burning Team with Emilie and Durin. Emilie helps with Burning while Durin can shred Pyro RES. Dehya triggers her Pyro application while the true C6 Pyro Traveler is the main DPS.
- Aether x Navia - similar to Noelle's case, they fit better in a Lunar Crystallize team with Bina and Zhongli
- Aether x Citlali - As mentioned above, Pyro Aether can be the main DPS but if he has the true C6. Citlali allows him to make a Melt reaction, shredding Pyro RES. Faruzan helps with her Burst and the effects of Viridiscent Venerer. Xilonen heals and shreds RES.
- Aether x Columbina - They have a lot of teams where they can be together and still be good, but their best team is in a Hyperbloom wheelchair with EM Ineffa. Kokomi helps with more Hydro apply.
And yes, they have memorable moments in almost all Sumeru events such as Ruins of Exploration and A Parade of Providence. Also their hangout event shows their closeness too. Layla gives the vibes of her being exclusively shipped with Aether and nobody else.
(Considering Nilou already has Alhaitham or Cyno, the Layla has Aether and nobody else)
- Collei - She is the Sumerian Amber. She's the one who welcomes the Traveler to Sumeru. She's the first Traveler's Sumerian female friend. And in almost every quest or event that involves Sumeru, the Traveler always finds her first and does things together with her. Even they always have a small chit-chat when they can't spend long time together because of their duties. The only problem with Collei is that she still can't physically touch anyone because of her trauma with Dottore. Let's hope that sometime, she can finally touch the Traveler with full confidence.
- Layla - She's the Traveler's closest Akademiya student. As shown in her Hangout event and in Sumeru events, the Traveler spends some time with her. Unlike Collei, Layla can touch the Traveler with confidence. And also, Layla has an alter ego, the Night Layla, who interacts exclusively with the Traveler. This is further reinforced in events like "A Parade of Providence" and "Ruins of Exploration". In one of the endings of her Hangout, Layla ends sleeping on Traveler's shoulder.
- Dehya - She's the only Eremite who is close to the Traveler. One of her memorable moments is making a peculiar contract where the Traveler pays her with a smile instead of Moras to work together in the Nahida rescue team. Also, she's the one who freed the Traveler from being imprisoned by Azar.
Which one is the closest Traveler's playable female friend?
After all, they are the two Traveler's main girls from Teyvat. (Main girls from Natlan and Sumeru, respectively)
Firefly, his main girlfriend from Stellaron Hunters/Penacony and Castorice, his main girlfriend from Amphoreus.
(Scenes made by Achevo)
Why Layla over other Sumeru girls?
- Because like Keqing and Ayaka, she has vibes of "Just for you". (Other girls such as Nilou have also popular ships that are equal or outclass Aether's in popularity. Nilou's popular ship is with Cyno, Alhaitham, Kaveh, Tighnari and even Sethos, which are equal or even more popular than Aelou, while Layla isn't popularly shipped popularly with anyone else than Aether and the Night Layla is a prove of this)
- Their Hangout Event proves their closeness, similar to Noelle's.
- She is the one who has the closest physical contact with him. Just look how many hours Layla would spend time with her head on Aether's shoulder.
- In Layla's voiceline, she wills to travel with Aether around Teyvat if she can't study anymore in the Akademiya.
- In gameplay, she can shield Aether to protect him from attacks (Especially if you play DPS Pyro Aether)
- As seen in Ruins of Exploration events it appears that in all Sumeru events, Aether will always meet Layla in a longer time than the others.
Source: https://www.pixiv.net/en/artworks/118735062
Nilou's main boy is already Cyno, so, Faruzan and Layla are the top Aether's girls.