You fall in love easily when someone shows you even the tiniest bit of affection. This caused you to fall head over heels for Rob when he held open the door for you. You were crushing on him for months now as he suddenly approached you and said:

I'm not into you at all. You give him a confused look. He looks at you.

Sorry wrong person. You brush it off and you both start talking and start hanging out. A few months later he tells you some news. I'm in love with you...