The thing with meljayvik is. Jayce really does love both Mel and Viktor.
Like the way he admires Mel and believes in her, the way he trusts her and turns to her for comfort (the way he apologizes immediately after their one fight). Mel has a very solid claim on his heart.
And obviously Viktor. They save each other's lives, their love saves the world, etc. Big cosmic love story.
The show repeatedly draws visual parallels between Mel and Viktor, but that's the thing, they're parallels -- they occupy a similar space in Jayce's mind and heart.
And they're not *really* in competition with each other either. Of course science and politics compete for Jayce's attention, principle and pragmatism, and Viktor and Mel represent those things on a grand narrative scale. But when Viktor is dying Jayce doesn't abandon Mel for him, he goes to her for companionship and comfort. And she doesn't keep Jayce to herself, she tells Jayce that the best thing he can do is spend time with Viktor. When Jayce *does* choose science over politics at the start of season 2, that doesn't change the relationship he has with Mel, they still have this very close and sweet partnership. And in the end, Jayce "dies"(?) alongside Viktor, but he never stopped loving Mel.
I don't have a source for this so take it with a grain of salt, but I saw someone say that in early drafts of the show the Mel-Jayce-Viktor relationship was a very kind of typical angel-and-devil-on-Jayce's-shoulders, which-one-is-he-going-to-choose type of thing. And there’s definite elements of that in the story. But you can also see how much the show ended up subverting that trope and giving the characters so much more depth. It's not Mel who ends up changing Jayce, he ends up bringing out a softer side in her, and rather than forcing him to reject his idealism she ends up trying to defend it ("I won't let them corrupt your dream"). It's not just that Jayce starts spending less time with Viktor (while using his political position to keep Heimerdinger from destroying the thing that might save Viktor), it's that Viktor also starts shutting himself off from Jayce as well.
What sparked this post is that I like a lot of jayvik fanart, but whenever I see fanart that builds out a broader story and world around them, I'm always like, okay but where's Mel? Or when I see a jayvik post that talks about Viktor as Jayce's one true love, it's like... nah that doesn't ring true.
Like Jayce's characterization genuinely falls apart if he's not also in love with Mel, imo. Him looking at Mel with heart-eyes, and telling her "you were always right" and "you will never be a passenger", and finally being able to relax when he rests his head in her lap, are all really important things about him. He gets into this thing with this sexy femme fatale, that's full of political intrigue, and then he’s like, I'm going to fall in love with her. And not only that, I'm going to assume that she's in this for love as well, that under her sharp exterior she's as soft and caring as I am. And then she is! And that's SUCH an important part of who Jayce is.
Because that's his approach to Viktor too. In the end, that's what it comes down to. Viktor had all this shit going on, and Jayce is like, okay, I'm just going to love you. And it works!
Jayce isn't someone who picks and chooses who he loves. For both Mel and Viktor, he loves and trusts them, and when he shows them that, it brings out the best side of them. For all of Jayce's weaknesses, that's his great redeeming quality, that he loves so genuinely, and making him choose between Mel and Viktor ruins that.
So yeah. While it's possible to just focus in on jayvik or meljay for particular purposes, I think if you zoom out and think big picture, meljayvik is the only way to go.
