That's not necessarily true.
First of all, bear in mind Mila from what we've seen so far has the yandere aspect sure, but also is arrogant, and the story gives the strong impression that this is a girl who got pretty much everything she wanted, pampered by (her grandfather) Victor and his organization.
So if the story takes a turn that Victor pretty much gets in trouble (and Lyk4n has already begun spreading the crumbs of that direction it seems given recent 2 updates), it could very much be that Mila may be placed in a position that she has noone else to rely on other than MC.
Of course, story might not necessarily go that direction, or it could yet Mila might still act out (demand that MC only sees her), but Mila changing herself due to circumstances can also be a direction.
Regarding board of characters, you're referring to that screen in the phone yes? This one?
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Tbh, that doesn't really mean anything for me.
There's already another game, Ataegina which had the board of characters (i.e. LIs) starting from it's Act 1, but some characters on Act 1's board basically became nothing more than cameo/one-off like characters, and with Act 2, new LIs got added, and the dev decided not to update the board (deleting the no longer relevant one-off flings, who initially players might have thought would have been LIs, and updating with new added ones).
In the end, nothing is set in stone.
On one hand, you could be right and Mila may be not a LI.
But on the other hand, it can very easily be said she most likely will be as well.
Other than phone's characters screen (which I think, as I said above, can mean anything), a lot of what's shown of her character (her long history with the MC, quite a bit of screentime put into her despite coming in late into the game, and not to mention more sex scenes than a lot of current main LIs), in my eyes points far more towards her being a LI than otherwise.
So unless Lyk4n puts his foot down and says "Mila's not a main LI" (like he did with the whole Mika Netori debacle. He pretty much put an end to that debate saying there's no Netori/NTR in this game), I think I'm gonna stick with it's most likely she's one of main LIs.
p.s. Just my though but there could also be an in-lore reason as to why Mila isn't in that characters screen lol.
It's because of security.
I mean sure, part of phone's function is to be a lore dump, but it's also used for MC to communicate with others. And so far, only messages MC has had with are with characters who are considered "safe" (i.e. people from his work, or those he lives with, or his mom's secretary).
Mila being in Victor's organization, it makes perfect sense for MC to not have her contacts, and iirc, she called MC. Same with Victor himself, who I think called MC at least once.
Given his mission, it's better to be safe than sorry by not having those Victor organization members (which includes Mila) in his contacts, rather than risk it and being found out by any of his friends who might inadvertently access his phone (So Zeke, despite not being a LI, is in characters, because he's "safe." Characters like Mila (likely LI), Victor (definitely not LI lol) are not included because they're "not safe").
