I have an iPad 2 and something weird is happening with iMessage. I can send messages to my friends, but sometimes after I send the messages it doesn't say delivered at the bottom and my friend says she didn't get the message. She's moving to Hong Kong and I want to keep in touch but all she has is an iPad mini. I'm not even sure if she gets my FaceTime either.
iCloud is having some iMessage issues as of late. I've had the same problem. It does eventually work itself out as Apple is aware and addressing it. However, at the moment they're stating all their services are up.
check here if you're curious https://www.apple.com/support/systemstatus/
I disabled iMessage/iCloud on all my devices (and my fiancé's [compare to you and your friend]) and then re enabled and it started working again. Have you tried that yet?