You are falling when:
1.) You blush and heat up when you're around him.
2.) You always stare at him.
3.) You think he's cute and like something about him.
4.) You're in denial.
5.) You dream about him.
6.) You can't get him out of your head.
7.) Your best friends notice.
8.) HE notices.
9.) He teases you and you like it.
10.) You always want to be perfect.
11.) You try to act like you always do, but doesn't work.
12.) You write about times when you've interacted with him.
13.) You're jealous when another girl 'sweet talks' him (Not always).
The list could GO ON AND ON. Just a few tips. Trust me, I speak from experience. Unfortunately...
Anyway, this is my cycle:
Blob-He's in your head and you think about him. However, you usually like someone more.
Crush-You definitely like him and you know it.
Boyfriend-You're openly dating him. Congrats~ <3