Silver lining and where to find it.

[Brian]

Likewise, speaking as a native, the phrase "There's a silver lining to 
every cloud" OR "Every cloud has a silver lining" is so much a part of 
our culture that I cannot imagine JKR meaning any other type of 
metaphorical lining.

The bad thing  (the big black cloud)  -  they are going to be separated 
and Harry will being danger
The good thing  (the silver lining)  -  at least he won't find someone 
else and forget her

Brian