How/when did you know you were in love?

I've worked with this guy for a few months but just recently started dating him for about two weeks. I have never felt such a strong connection so quickly. He has gone out of state to visit his sister and it has only been a few days and I feel like I am incomplete without him here. I miss him so much and I don't know if this is healthy or not. I have never felt this way about someone so quickly, let a lone miss someone this much. I don't want to say I already love the guy but apart of my feels like i do. When have you guys figured out you love your SO and what made you know you did?