nathsketch:
And this is the part of Xiang Liu:
I'm guessing each of the people represented by a wide cylinder shape instead of a circle is one of the Emperors from Once Promised. The Flame Emperor of Sheng Nong on the left in red/brown. The Yellow Emperor of Xuan Yuan at the top in orange. And the former Grand Emperor (Shao Hao's father) of Gao Xing on the right in blue. Although it seems strange that Ah Heng is not directly connected to her parents.
XY is linked to a person who is neither red-brown nor blue, but something in the middle, with two linked circles. That must be Feng Long (a Sheng Nong descendant who becomes loyal to Xuan Yuan and even fights for Xuan Yuan against the Sheng Nong remnant army) and the two linked circles must indicate a relationship where the two were only engaged but never married.
A filled-in heart links XY to TSJ in green. I assume the link between TSJ and Feng Long indicates that they are friends.
A filled-in heart links XY's mother (Ah Heng) and father (Qi Yo / Chi You / Chi Chen). They were never married, so filled-in hearts can't represent marriage.
Filled-in hearts also link the Yellow emperor with two people at the top of the chart. Presumably Empress Lei Zhu on the left and his favourite consort on the right. My understanding is that Lei Zhu and the Yellow Emperor did love each other once, but he later favoured one of his other consorts.
I'm guessing Ah Nian is the top blue circle and she is connected to Cang Xuan by a not-filled-in heart. I can't tell clearly, but it looks like Cang Xuan might also be linked to XY with a not-filled-in heart. And Cang Xuan's parents are linked by a filled-in heart.
I'm guessing the middle blue circle is Shao Hao (who became Grand Emperor after killing his father). But I'm not sure who the bottom two blue circles would be. Maybe they are his other two disciples, Ru Shou and I'm forgetting the other one.
Not-filled-in hearts can't represent one-sided / unrequited love if the chart acknowledges that XL loved XY and that XY loved XL back. But it somehow has to work for CX and XY and for CX and Ah Nian too. Ah Nian loved CX romantically and married him, but CX only loved Ah Nian as a sister...
So my guess is that the filled-in heart represents romantic love that is openly acknowledged by both parties and "fulfilled" in some sense (e.g., through marriage or having children). While the not-filled-in heart represents mutual romantic love that isn't openly acknowledged by both parties or mutual affection where one side has romantic feelings and the other side only has platonic (e.g., sibling) love for the other person.