Because I know it's going to happen, and I want people to know it's going to happen, but I'm worried about people clicking and being disappointed that it hasn't happened yet and that that tag is somehow disingenuous for that chapter.

As a reader (and I feel most readers in general) and smart enough to know that if a fic is tagged as character A/character B and it's a multi-chapter, they're going to automatically understand that even though the two character might not be together in the beginning, CLEARLY the fic is going to be about (or have a subplot about) them hooking up. I mean, that's just how stories work.