By Galactaea
 

He'd probably be discouraged. Florian, judging by her personality, would probabluy get annoyed by Gallien at first anyway, regardless if eventually they did become a thing.

By Galactaea
 

Then make him more awkward than usual around Florian. If Sissy says no, then Florian will refuse.

By Galactaea
 

Sissy hasn't replied yet. You can make Gallien have a crush on Florian, however, but they can't become a thing unless Sissy gives the ok. Doesn't mean Gallien can't be annoying and follow Florian around XD