It may have been better to have kept this to your other thread on this issue. You did the right thing in separating them when considering the comments and information you provided and received on your other thread.
They need to get used to a new way of living and that may be why he is quiet. They still are able to interact through the bars so that will stave off loneliness. Having a new friend for each will of course help for the longer term
I have merged your two threads as this is an ongoing case. Unlike social media, we have to option to run an ongoing support thread on a specific case for as long as necessary to provide tailored advice and individualised support.
The bullying piggy is always very upset with a separation. They very much rely on companionship but like a small child cannot understand what they are doing wrong - and this is not something you can explain to a guinea pig; even less so than a child!
Could you move the cages together so they can interact through the bars all the time?
Here are some enrichment idea to help perk up Cookie: Enrichment Ideas for Guinea Pigs