Plot wise this is what I can remember, although I'm not completely sure where the first, second, and third parts of the arc begin or end. LOL my memory is not that good.
Milliard is a young boy, probably about six. It unfolds the tale of how Milliard lost his family and everything he had ever known to a terrorist attack on his family estate. He changes his name, because it reflects the age and position he was at the time of the murder of his family. He ends up being jostled from place to place until the Kushrenada family opens their arms to him for the holidays. (end part one?)
I want to say that Milliard is about 14 or so, while Treize is 16 or 17. I think that Treize is just entering OZ and is heavily influenced by what he has seen in the training academies. We discover that Treize has a crush on his younger companion. His mother is really cool in the arc too. They talk about her being from gypsy blood and she is slightly psychic. Anyway his mother warns him that Milliard is young and impressionable and not to push his desires on him. She makes a comment about that Milliard needs friends more then lovers. There are a bunch of shonen-ai cute scenes with them visiting what I want to say is Prague or something like that. A lot of Kushrenada family members converge upon the estate and they make comments about Treize's sexual preference and rudely suggests that is why he is friends with Milliard. Milliard is confused by all of this and asks Treize when they are alone. Treize dodges the question by giving him some sort of yaoi doujinshi book to read. After reading it Milliard is still confused, but understands that it is basically boys kissing other boys. He asks Treize if what Treize's cousin said was true. I can't remember the exact words, but he says that he cares for Milliard, but leaves it sort of open ended. Somewhere along the way the boys go on an outing and get really close to kissing and some how Treize hurts his foot. Later that evening they are playing truth and dare in Treize's suite. The first round Milliard is dared to confiscate one of Treize's cousin’s panties and Treize has to tell the truth about his feelings for Milliard. The second round Treize dares Milliard to run down stairs and take a shot from room where the adults are are; Milliard dares Treize to kiss him, which he does lightly on his forehead. Milliard is frustrated and unsatisfied and pulls Treize down for a proper kiss. Milliard leaves to go back to where he was staying, promising that he will make Treize proud to love him. (end part two?)
Years later Treize's mother is dying, I think from cancer. He comes home from OZ to take care of her in her last days. I think Treize is 19 or so. He gets a visitor at the estate while he is shooting clay discs in the snow. A stranger comes up and asks to try his hand at it. Treize lets him and comments on his superb marksmanship. The stranger says that he wanted to earn the respect and love of someone very dear to him, so he joined OZ and poured his heart into being the best. (Obviously not in those words ^ ^) Treize can't believe it is Milliard, age 17 or 18, and insists that he stay with him until his mother passes. A lot of Kushrenada families visit the dying woman, including a young Dorothy, who does her best to spoil any of Treize and Milliard's alone time. In a particular instance Milliard tries to wake Treize up one morning, only to be pulled into the bed. Milliard finds himself underneath a very naked Treize, who is very happy to see him. Dorothy comes in the moment that Milliard works up enough courage to go past foreplay, and ruins the moment. Eventually they ditch the pip-squeak and screw like bunnies in the spring time. A few days later Treize's mother takes a turn for the worst and dies, but not before giving her blessing on their budding relationship.
Also I am pretty sure that that author calls Milliardo by Milliard. If anyone has any idea who wrote it or where it can be found I will be most grateful.