This is the first book, Red.
There are also a second book, Black Iris, with a bad ending, and a third book, White Joy, with a happy ending.
The second book came first, but the writing is so childish ( ・᷄ὢ・᷅ ). The third book, White, is decent enough. I'll post it too when I get the time.
Here's the blurb for this book:
Old wounds have yet to heal, and new blood keeps flowing.
My junior apprentice brother was like a spirit in the snow, dancing in my heart for years.
But that day, the blood beneath my junior brother bloomed across the bone-chilling snow, like the red roses on our wedding day.
"...We just want to live."
Theme: Love is an entanglement of two lives bound together, unable to let go
It's really, really beautiful, I like it very much