A has some news to tell B, and wait in their apartment, waiting for B to get home so they can tell them. When B get home, A tries to tell them, but ends up breaking down in tears. It's only after the subsequent confused cuddle session that A manages to tell B. Crying and kissing and holding each other ensue.

Angst?
Disease?
Miscarriage?
Death of relative?
Depression?

Fluff?
Pregnant?
Got new job when they're in debt?
They found the engagement ring B was planning to give to them?