Where to find the song that is basically "next to you" played with a different instrument? In Episode 8 at 10:40, when Shinichi throws the dog in the trash, a song plays that I have not been able to find anywhere on the internet.

I know the song is basically "next to you" with a different instrument playing it, but I want to know where I can find the whole song played with that specific sound.

The original "next to you" OST just does not give the same sad feeling as this other song.
I believe that the tune you are looking for is Next to You-Anime Version. This one is different from the Original One in the aspects of being slower and softer, and with a totally different instrument playing it and from the other Anime Version in the same terms.

Unfortunately, I haven't been able to find it in any of the OSTs. It might be an unreleased track for an unreleased OST, but that's anyone's guess.