What does it mean when a text says Not delivered to a iPhone?

This guy I work with and I been texting each other since July 5. I'm trying to text him through my iPod touch and the text keeps saying not delivered but when I text him from my Samsung illusion (android) cell phone it gets delivered. Did he block me from sending him texts from my iPod touch? Btw he likes me because I talked to him on Sunday, August 10.

Maybe he has an iMessage problem with his iPhone. Since you think he likes you, you wouldn't have blocked you. He probably turned off his iMessage and that is why the message is not being delivered. Hope this helps.

Does he an Apple device? Or did he switch phones recently? If so he might have accidentally disabled iMessage therefore your iPod can't reach him anymore. You also might have accidentally disabled iMessage on your device. Only iOS 7 devices and above can block iMessages.

These might help:
http://support.apple.com/.../kb/TS4268
http://www.wikihow.com/Activate-iMessage