Satoru insincerely promising to change when Shun is breaking up with him in episode 8 and meaning it when he says it to Saki at the end of the series in episode 25

I love looking at dreamy wholesomechungus art of a female protagonist with two bishounen if it’s emotionally canon. This is why I am so obsessed with Lily Hoshino’s art of Shouma and Kanba doting on Himari

Obviously Maria x Saki is uniquely high-impact due to the particularly tragic circumstances of Maria leaving Saki for someone she (imo) doesn't love in that way and then dying offscreen, the fact that it has its own official song by Maria's VA, and most importantly half of the entire episode 16 just being a reading of Maria's love/farewell/apology letter to Saki, but one thing I really like about SSY is that really every pairing is legitimate, she does love Shun and Satoru.

Shun I do think will always be Saki's first love even though he lost interest in her in certain respects after they entered puberty-- even aside from the unique sociological worldbuilding of the show I think that Shun is probably more sexually attracted to men than to women (if indeed he was ever attracted to women at all), but Saki is the person he was always closest to in terms of his emotional experience of the world and the only person he could ever confide in right up to the point of his death/loss of self/whatever happens to "karmic demons". Certainly he was attracted to Satoru sexually but he grew bored with him quickly, and ultimately it was always going to be Saki he was waiting for in the lakebed when he died. What Shun and Saki both had in common even from a very young age was their curiosity and clarity of mind, but Shun was doomed by the fact that unlike Saki his intellect outpaced his emotional maturity-- in the end he was literally annihilated by his own mind. I like to believe Shun survives in some shape as a diffuse thoughtform, that when Saki and Satoru "hear" him it really is Shun appearing to them rather than just a visualization.

Satoru is interesting and at times a little frustrating to me... he's Saki's first sexual experience (Presexual I guess? They're clearly just experimenting with each other because they're isolated and stressed/afraid), but he seems to grow up so much more slowly than the other characters, except Mamoru obviously. He is very courageous in the traditional sense and willing to break the rules to stand with Saki, but he lacks Shun's raw intelligence or Saki's subtler resilience. He is always a reliable friend, but there's a noticeable disconnect between him and the rest of the group as the reality of their situation becomes clearer. As Satoru grows into a man I think he matures enough to understand this and turn it to his advantage-- he acts as Saki's emotional anchor and literal protector; he doesn't need to have Shun's genius or Saki's moral strength to stand by her both emotionally and physically. Do they love each other? Well, yes, but I don't know if they love each other in that way. I think Satoru will always be in love with Shun, and that when he and Saki have sex (probably a few times a year for the purpose of conceiving children, let's be honest) they're probably both using the other as a kind of conduit to Shun. Still, Satoru is always the person Saki leans on. His relative emotional stability means he'll never destroy himself the way Shun or Maria did, and more than anything else Saki needs someone to hold onto whom she can trust implicitly not to self-destruct. A lot of people like to think it's Maria's hand Saki is holding when she wakes up from the dream crying at the end of that ED, but in my mind it can only be Satoru. I'm glad they end up together.