I think the beauty of the YaoXuan ship is they they never got together romantically because I find the love they share is much more intense than romantic love. CX never needed to earn XY trust and love. She gave it to him in spade. He got something much more precious from her but too bad he didn't realize that.
Secondly, the both of them are incredibly traumatized kid. So I can't help but think part of their love is a by-product of trauma-bonding. I believe that CX is capable of getting the throne without needing to hand over XY to both FL and Jing, or him needing marriage alliances. But when the Haoling King told him he was not ready, he insisted. This show that CX had gotten very impatient, and this impatience had influenced his behaviors when it come to XY/FL/Jing. Not only that, I think CX have some fear in his heart as well. In front of him are two examples: The Xiyan king who married for power, and the Haoling king who devoted to one woman. He saw first hand the sacrifices they both had to made, and they STILL lost the woman they love. Not to say that CX will repeat their mistakes, but I think it did influenced him and prompted him to take the third route: if you never had your love, you can't lose them.
To be frank, I do not feel bad for the YaoXuan ship. I feel bad for CX. Both XY and him had suffered a lot as children for the decisions made by adults. But XY found a reason and someone to heal her wound, unconditional (to the point of irrational) love from Jing (and XL although she was not aware). But CX, despite wandering the world for 200 years, did not met his "Jing" and "XL". So he pin that love/healing on XY. So rather than wishing that he had picked XY from the start, I wished he had met his Jing/XL. They both deserve their proper "healing" but only XY did.