IDIOMS

L-bomb

(idiomatic) an expression of love, usually one that provokes a significant change in a relationship

Example: 2003 December 22, Joe Kita, Guy Q: 1,305 Totally Essential Secrets You Either Know, Or You Don’t, Rodale, ISBN 1579548598, page 139:
  â€œThen take her on a tour of places that are special to the two of you — the bar where you had your first date, the park where you dropped the L-bomb, [...]”