I think Lewis heart is a representation of what’s keeping him alive, what drives him and keeps him going.
So, ever since he showed up in Ghost he has a Yellow/Orange heart. Which is associated with Arthur.
“Why isn’t it blue like Vivi? He clearly loves her”
Because that’s not what’s driving him. He isn’t stuck here because he loves Vivi, he’s stuck here cause he wants Revenge on Arthur. He was killed by his best friend for no reason. So he restlessly chases them through Ghost. Until Vivi interferes. And when Arthur drags her away his heart breaks.
He was then driven by heartbreak and sadness, as you can see in his outburst and crying at the end.
In Freaking Out, we see Shiromori step on his heart and throw it around. Until Lewis finally snaps and punches her head off.
When he sees Vivi’s flower he gets hopeful, but as soon as he sees Arthur’s. Welp.
So when Lewis puts the petals in his heart, it heals because he finds hope to be with her again, then it goes back to yellow because he’s still going to get his revenge.
Finally onto Hellbent. Throughout this video ( all of them actually) you can see Lewis has 3 Dead Beats. A curious one (probably his ghost Hunter side) a angry one (for obvious reasons) and a sad one. Of course, he was betrayed, murdered and ignored.
I think Lewis thought he was completely forgotten. Neither Vivi or Arthur seemed to react to him other than being scared (you can see he’s clearly bothered just before he throws Arthur in the truck), and they didn’t seem to be missing him. So it makes sense he just “ignored” Vivi and mystery in this video, his reason to EXIST is getting revenge right now.
Then finally about the cliffhanger.
When Arthur punched the “possessed” van, I think his metal arm kept some of Lewis powers. So when he grabs his arm on the cave, he gets to see Lewis how he sees himself. Until that exact moment Arthur had no idea that pile of bones in a nice suit was his friend, as evidenced by him looking for him in the end of Freaking Out.
And when he realizes it, he is completely shocked. He says “Lewis” just before he starts falling. He realizes his best friend is dead, AND killing him.
In half a second, Lewis realizes what that meant. By the change in his behavior, Arthur didn’t know it was him until that point. He wasn’t faking any of that. He genuinely didn’t know Lewis was dead and now..
Lewis just killed his best friend. His heart filled with regret and grieve immediately cracks.
StalkingSangwoo 