People in your generation, the under 25’s, end relationships so quickly because for one thing, they have a lot more dating options today than their parents had.
With all of the social apps and social media sites a la Facebook, they have a wide variety of options in terms of meeting potential partners that many previous generations didn’t.
People in your generation are also in the age of instant gratification.
However, there are guys who will act like they don’t care about a girl much in order to make her feel insecure. There are guys who play this game.
They will essentially refrain from complimenting the girl in order to ensure that she keeps thinking about them. She thinks about them wondering why she is not being complimented.
If 
If he rarely initiates texts but replies right away, there is a good chance that he is not particularly interested in you. 
To write secret admirer notes, you should ensure that you stick to what you know.