It is shounen ai but it has no kisses or confessions more like bromance or how you feel all soft moments but nothing more. soft love. I won't even say it has any real couples
if you want just a little something more between charcaters try koori no mamono no monogatari by same author. It has atleast 3 or 4 kisses (=・ω・=)
it's full of bromance that's why this is shounen Ai, real couple? yes, but no kiss, no confession, more like shoujo. it's shoujo, shounen Ai for you.
Shounen ai but in a 'cockblocked by censors' way like how Xena and various other 'coded gay' series went.
So you get declarations of 'like/love' and wanting to be with them for always, dying together because they can't live without the other other and so forth. So the subtext is definitely for there for us to textually accept their relationship as canon.
I personally do not consider it shounen ai, as there is no official romance in the manga. It's just heavy BL subtext and bromance, but it never goes as far as to be canon. Which really sucks tbh.
The author wrote Silver Diamond with the intent of it being a Shojo manga. Some characters--namely the two main protaganists--are very close relationally to each other. That is how the author wrote the characters. They were not intended to be actual couples. However, the author does not mind it when fans consider them shonen-ai couples.
This is a shoujou manga or shounen Ai manga? Is there a real couple? Confession? Kiss??