What if, Fleur and Harry are together as a couple, but Harry wants no one to knows ans in Dumbledore, Voldemort, his friends, etc. There is only one person Harry trusts with that knowledge, his actual best friend/older brother figure Bill Weasley.
He can't bare to be without Fleur, but they have no good reason to see each other, and harry is under constant surveillance, so he proposes an insane plan, that Bill pretends to be in a relationship with Fleur, so she can be at the Burrow, where they can see each other.
They can't talk much, they can not touch too much, or intimately, and they can definitely not risk a kiss, so most of their conversations/emotions is conveyed through the eyes.