Is it this one,? http://www.mangago.zone/read-manga/canis/
ahhh Dx no but its pretty looking! ill edit my description if i rememeber anything else!
OH WAIT IM A FOOL, yes THIS IS IT!!!!!!!!! THANK YOU!!!!!!!!!!!!!!!!!!!!
You're welcome. lol I was about to say but it's pretty similar to your description It's understandable since they're not the main story.
http://www.mangago.zone/read-manga/canis/mh/5bab950ca56ecf9f/Ch19/pg-1/
It's a spinoff of some characters from Canis so the first person was infact correct.
i cant seem to recall its name! i remember there were three boys who were living in an orphanage with nuns, and there was this secret that like, three kids would go missing each year? i remember they all got adopted but wanted to stay together, but in the end went their seperate ways and the story branches off from there. i remember the blonde boy was named sam? i think? the blonde boy was really smart. i think the manga cover is a black haired guy with the other two laying next to him seemingly on a bed? i think?