Hi everyone, I'm so sorry it's been so many years and I don't write stories anymore. However I do understand the feeling of not getting closure with a story you've invested time in.
It's not very satisfying and I had to re-read the story to remember it but I think this is what I plotted many years ago for the story:
Let's start with the villain characters:
*Yuuki has been obsessed with Kaname since she met him at a party as a young girl.
It's obsession and not love because she raped him and forced him into an engagement against his will. Kaname does end up marrying her but divorces her when her plot with Rido is uncovered, he also shames her and makes sure everyone knows what she's done.
*Rido is one giant psychopathic pedo. He has an unnatural obsession with Zero and killed his wife and child to be able to force Kaname into becoming the main "heir".
He does manage to convince Zero to date him during Zero's moment of weakness as Kaname's wedding prep continues and of course during Kaname's marriage to Yuuki.
He also sleeps with Zero and was going to kill both of them to be able to "keep his happiness eternal". It's creepy and wrong and he considers it love but it's really just possessiveness and him not wanting Kaname to have any part of Zero.
He meets his end with a bullet to the chest. When all his plans were uncovered Kaname confronted him and as he was about to kill Kaname, Zero came into the room with a gun and warned him not to. He decided that if Zero kills him, he'd always have a piece of his heart and will never be forgotten so he forced Zero's hand into shooting him. Psycho till the end.
Now the main characters!:
*Kaname has always and will always love Zero. He absolutely hates himself and his life without Zero. Why did he not just throw everything away to be with Zero? It wasn't being the heir that held him back, it was the fact that he betrayed Zero and was disgusted with himself for sleeping with Yuuki. Miscommunication + self-loathing with a dash of evil uncle and crazy stalker plans = one unfortunate Kaname.
He was filled with jealousy when Zero started dating his uncle and when he found out that Rido and Zero slept together he attempted suicide. Honestly Kaname's the most victimised character in the whole story. With the help of the loveable misfits a.k.a detectives Aido, Maria, Ichiru and Sayori, Kaname was able to uncover Yuuki and Rido's plots.
After Zero killed Rido, Kaname confessed everything including what Yuuki did to him and why he felt he couldn't go back to Zero. He finally gets Zero back in the end and is happy for the rest of his living days.
*Zero our beloved little mochi goes through a lot. He tries to put on a brave front but can't handle the fact that Kaname's getting married so ends up making some very poor choices (as was Rido's plan all along). He ends up giving in to Rido's persistence and confidence and dates him. He actually enjoys the dates and for all his crazy, Rido treats him very tenderly when they're together.
Zero goes to Kaname's wedding and afterwards sleeps with Rido because he's trying to physically find closure from his feelings for Kaname. Actually there's a small part of Zero that was beginning to have feelings for Rido until Maria told him everything. Zero realises that if Kaname knew then the first thing he would do was confront Rido.
Zero takes bloody rose (his gun) just in case and races to find both men. He warns Rido not to hurt Kaname or he'll shoot him. One of the things he says to Rido is "was everything a lie, did you even really love me", after which Rido smiles and tries to kill Kaname to force Zero to shoot him.
After they clear the air between them, Zero and Kaname are finally able to be honest and forgive each other. They've been in love since they were children and they stay together till the end of their life.
So that's the happy ending, the original ending I would've written if I kept the original title "sometimes it's too late", was going to be Zero marrying Rido and being blisfully unaware of all his crazy. Kaname constantly trying to get in the way of that relationship out of jealousy and failing because he's married Yuuki and is trapped. Rido trying to keep Zero happy for the rest of his life and shoving his love filled marriage in his nephew's face every time. Maria hiding all of Rido's plots and the skeletons in his closet because Zero's happy and that's all that matters to her in the end.
I hope this was able to give some of you the ending that you may/may not have wanted!
All the best as well and hope you're all keeping safe during these days!