I know your comment has some dislikes, and people may see it another way, but I genuinely think that you have a point to make, specifically about how Rian can be so misleading and deceitful towards Cadgan and Hector both. 

(spoiler warning for the story in both comments btw)

~-Understanding Rian-~

- By me -(o.o)-

I will expand more on it. Please hear me out: In the sense that I, too, think that Rian is at fault for many misinteractions as well. At first, I thought his dialogue was sweet and endearing. I was starting to think being 'TeamRian/Ranzkai' was the way to go about it... But, the more the story advanced, the faster I realized he IS lowkey a bit messed up. Even if he didn't mean for it to come out that way, the things he says and does are suspicious, and I truly get what you think, but then, and here comes my thought about it...

I mean, who wouldn't be at least a little messed up on his shoes to begin with? I think that we first need to understand how it was for him from the moment his existence began; all he knew was darkness, and then, when he gained a semi-transparent physical form, he held nothing other than the past disgust, wrath, rage, and fear Cadgan made him hold. I mean, what other choice did he have? None of course. Then came the years together with Cadgan alone. Rian learned from the memories of the past Cadgan, and surely he could soon speak and do stuff for himself as he possessed control of their body, but things were quick to become different as someone else got into the picture, and that being, of course, Young Hector. 

For Rian, at least at first, he was just another small, unknown boy. But as Hector kept trying to get to know him and get closer, Rian found himself observing the badger with caution and something else he couldn't name. Because he never felt it. Nor did he knew he could ever "feel" more than the stuff Cadgan led him carry. Days passed, and in between walks around the manor of the duke, and medical examinations/visits, they would converse more. At this point, Cadgan, of course, would soon start pretending to be Rian once it was his turn with the body. This "Clinical Letargy"  illness was more so by the fact that their mind, both Cadgan's and Rian's, were severed, unwilling to commune together in the same body. Cadgan refused him and hated him after all, back then, of course. A few days passed, and finally, the walks and hangouts on the lake happened between Rian and Hector. 

Right up to that point, they discuss more about their past. Rian would get flashes of Cadgan's memories sometimes due to their shared connection, and then he would become too sad and start crying each time; he didn't know how to control it, of course. It was then that Hector would proceed to comfort him with his calm and quiet presence, and just then, we read about how Hector meant a lot to Rian in those little moments. And the moments that would follow afterwards. And then those moments, too. They start playing together, Rian teases him sometimes, and Hector would humor him gently. 

And then we get lines like, 

When he wishes Hector's words weren't so shy,

Hector says to Rian that he can have a place beside him if there is none for him in the world. And the deciding one from Rian to Hector in his thoughts, something like;

"When Hector is around, the world makes sense, and the question of whether I'm Cadgan or Rian stops mattering. Because whatever I am, it might be alright if he's near me. If we can keep laughing, and make new smiles, then maybe I won't need to yearn for old ones anymore..."

They would then pass on to become close. Hector would start feeling things for Cadgan, thinking he's been hanging out with him all along. This wasn't true for the most part, Cadgan didn't really think anything too romantic when hanging out with Hector.

And then months passed, and as Hector left to accompany his father, Rian never forgot Hector. In fact, he seemed to acquire a fascination with the Badger. It would then turn into ramblings about him, the sent letters, and everything. 

I can take all of this as evidence to prove that, not only Hector, without meaning to, helped Rian understand that there were times he could feel at peace, but also proves that Hector would go on to become his sole, truly good experience ever since he began existing. The moments with Hector marked him for life. 

If you take all of this into account, Rian wanting Hector all to himself years later starts making way more sense. Curiously, one of the only times we see Rian speaking with the use of "Us" or "Our", that is, including Cadgan too, was when Rian said to Cadgan, "Our boyfriend," referring to Hector, so that's that...

Conclusion;

 I think deep down, Rian fears that Hector would start loving Cadgan too much and drive all the attention away. And on the contrary, that Cadgan would also love Hector back even more.

I needed to show my understanding so far, at least from my point of view. 

Thanks for reading, love y'all that beared with me in this long ass message😭😭💕

Oh, so many dislikes. I understand why many people hit that button, many see that relationship as """"cute"""", but I see your point. Maybe you are right, but we need more context. I'll explain by points:

SPOILERS AHEAD

1-- Rian was born from what Cadgan rejected: fear, sadness, love for being a priest, and rage (but later Cadgan recovered that rage and redirected it toward Rian while he was still kidnapped by the duke). So those were the only things Rian could feel. When Hector appeared, they started seeing the world in a different color, and all of his fears disappeared, so his love was born from all the negative emotions he carried.

"When Hector is around, the world makes sense, and the question of whether I'm Cadgan or Rian stops mattering." "Because whatever I am, it might be alright if he's near me. If we can keep laughing, and make new smiles, then maybe I won't need to yearn for old ones anymore."

2-- Continuing the previous point: Rian doesn't want to lose Hector. Hector is like a patch, or better said, a drug that covers his pain. That's why he is so obsessed with him and acts very possessively, using "I/me" when talking about Hector and rarely "we/us." He does use "our" once when calling him "our boyfriend" while they were spying on Silvareth, but the context is a little tricky: that night it was actually Cadgan who was with Hector, not Rian. So Rian is using Cadgan's intimacy with Hector to include himself, and claims him as "ours" only when it's convenient.

3-- Cadgan is more cold-headed because he doesn't carry all those emotions, making him more reasonable than Rian, but also less emotional about Hector. Cadgan doesn't see himself as worthy of love, or doesn't see it as important enough, which is why he tried to reject Hector. He is probably denying his own feelings, or at least letting Rian love Hector for both of them. So we can say Rian loves Hector freely precisely because Cadgan is rejecting his own feelings, but he never consciously passed that feeling to Rian like he did with the others before. Also, Rian was trying to convince Cadgan to be with Hector (because he knows that Hector remembers Cadgan's face), but Cadgan didn't show much interest, either out of denial, or because he genuinely doesn't know how to act in those situations.

4-- We can't forget that Rian changed physically, but Cadgan didn't. Hector remembers Cadgan's face but has never seen Rian's, so that's likely why Rian uses "I/me" all the time. It may be his way of affirming his individuality apart from Cadgan, and his desire for Hector to recognize him purely by personality.

5-- Last but not least: we don't know how the author views relationships, whether he sees them as traditional or open. The novel establishes that Cadgan and Rian are the same person, but also that they are different. So Hector loving both of them is, in theory, a polyamory relationship, just like Venom and Eddie with Anne. Maybe when the novel is finished, it'll end with Hector with just one of them... or both.

~~~~~~~~~~~~~~~~

I'm not saying Rian is manipulative, but he is childish, throwing tantrums whenever Hector is involved. He's like the kid in the neighborhood who says "the ball is MINE and I decide when YOU play", except the difference is that Rian doesn't even realize he's holding the ball. The love Rian shows doesn't seem healthy anyway.