Everyone is self-centred - everyone, bar none. We are each literally the centre of the universe in every way that we can see and hear and feel. It takes active, conscious observation of the world around us, and active, conscious modeling of that world as a separate thing which exists independently of ourselves, to counter that foundational solipsism.
Our MC seems self-centred for a number of reasons, but the biggest one is that she's in the middle of a literal existential crisis - she's struggling to make any kind of rational judgement as to the reality of the world she's in and the people around her, so all that she has left is her own sense of self. But that's taken massive damage as well, because she's got memories from two different lives sloshing around in her head - on top of that, one of those lives includes memories of a different perspective on some parts of the other life (from playing the game). Everything around her is coloured by that, and the only way she can handle it is to focus inward, on herself and on her own direct observations, while she rebuilds her understanding of the world around her.
The game's MC . . . . . is just childish. He hasn't fully developed that model of the world around him as a separate thing that has its own independent existence, and as a result he's got a strong tendency to see the way that things have happened in the past as being the way things should be - his childhood friend making him lunch every day is just how the world works, and the fact that it's a conscious choice by someone other than him doesn't seem to have registered. The way he's reacted to the world changing reinforces that assessment - the rational response would be to accept her decision and move on, or (depending on their relationship) to negotiate or plead with her to change or something like that, anything that recognises that she has her own separate existence which he should respect; instead, he's basically just whining about how he thinks the world should be.
One of them is in a position of massive disruption and uncertainty, the other is simply being exposed to the normal minor challenges of growing up . . . so yeah, just some slight differences between the two.
How they progress from here will be interesting. They both have the same choice: head further down the solipsistic self-centred path (for different reasons, and to different ends, but with the same underlying cause - not being able to see the world around them as truly real), or engage with the world more fully, and interact with the people around them with the respect they deserve . . .
