Signs of falling in love?

Does anyone knows how to tell if you fell in love with someone? I wondered about this for quite some time and I still can't figure it out.

There were some guys I liked, but now I think I just liked them as a friend and nothing more. I also am single since... ever... so I don't really know how 'love' feels.
Recently I've been thinking about this one guy, but I don't know if I like him that way or not. I'm still thinking "That's not love!" until I'm completely sure about this.

What is love like? How do I know if it is love?
I hope someone can help me or just share their love stories with me :3