Your title and question is confusing: is it nothing at all being sent repeatedly or this one time? Restart your phone. If that doesn't work, take out your sim card and put it back in. Then restart your phone. You can also try a different messaing app if it continues to not send. Do you have a good network connection?
Try texting someone else. If they receive your text then I would assume that your friends phone/service is the issue. Also make sure you are not texting a landline, sometimes you will receive a message stating it could not be sent.
If neither of those are the issue, It could be related to your plan or your service coverage. Does your friend live in the same province? If all problems persist just restart your phone like Goran mentioned or try texting them in a couple of hours to see if the issue still exists. It could just be a network glitch.