I threw myself into a discussion some AnK fans were having to voice some of my own opinions. I just copy pasted them here, and now I'm going to attempt to edit it into some sort of out of context coherence.
I don't have any deeper thoughts regarding how Guy behaved towards Riki, but I did kind of get the sense that Riki loved Guy because he was safe, and familiar. It was love, but not love.
Meanwhile I'm not certain if his feelings for Iason were actually love, or if it was really some effect of getting traumatised by Iason.
If it was truly love with Guy at one point, it might have been that overwhelming love that teenagers have, that you then as an adult wonder "What the heck was I doing??"
It might have been true love for Guy
Or maybe because Guy never got to leave Ceres and experience more of life outside of the district he might still be stuck in that safe, teenaged love.
I think Guy was also so deadset in his knowledge of who he knew Riki was that when Riki had suddenly started changing, making choices that didn't involve Guy anymore, he refused to understand and adapt to a new Riki who had learned things and grown in ways that Guy had no idea about.
So when Riki finally just outright told him he was choosing Iason, Guy absolutely knew Riki must be brainwashed or controlled, because the Riki that's in Guy's head would never say such a thing
The whole thing feels a little bit like a horror story telling with the subtext of psychologically breaking out of terrible situations and dealing with people who are worse (tanagura), and the people who are still stuck in it (ceres)
So basically an allegory for breaking away from abuse.
There will be the awful, manipulative people who want to keep you the way you were, under control, "weakened", which is Tanagura.
And the people who haven't managed to break away yet and are still stuck in the mindset and how you see them after your own situation and outlook improves, which is then Ceres.