Why is my iphone not sending messages?

I'm trying to send texts to my cousin who has an iphone and has the same carrier.every time i try to text them it tries sending the message and when it gets to the end of the status bar thing the message just disappears like it was never there.
and it only does this for this one person.
why won't it send?

Probably because iPhones suck buy the samsung galaxy s3 or note2

My did the same thing try turning off iMessage in the settings

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