Crush aired for BTVS season 5, episode 14. This is a Spike-centric episode with lots of crushes revealed. At the start of the episode Spike is dating Harmony. (Harmony is shown above pretending to be The Slayer in Spike's bedroom.)
Over the course of this episode the viewer learns of several crushes, and several romantic relationships change. Dawn has a crush on Spike. Dawn reveals to Buffy that Spike has a crush on Buffy. Dawn used to have a crush on Xander. Drusilla returns and Spike professes his love for her, dumping Harmony. Later Spike professes his love for Buffy, offering to kill Drusilla. (But also he threatens Buffy that he'll let Drusilla kill her.) Harmony and Spike fight, Drusilla and Buffy fight. The episode ends with both Drusilla and Harmony dumping Spike and leaving. Buffy also punches Spike and leaves. Buffy later revokes Spike's invitation into The Summers house.
During the episode Spike and Buffy spend time together and Spike acts differently towards Buffy. (Note his unusual-for-him dress in the photo above, where he is sitting in The Summers kitchen.)
BUFFY: What … is this? The late-night stakeout, the bogus suspects, the flask? Is this a date?
SPIKE: A da- Please! A date? You are completely off your bird! I mean... (in a much quieter voice) Do you want it to be?
Buffy reacts with disgust and is upset at the idea of dating Spike.