Hello lilly317,
After reviewing your post, it sounds like there is trouble sending text message to one specific contact. There are a couple things you can try that may be able to help. You could try creating a new conversation and sending another message. You could remove the contact and recreate it. I would recommend you use this article to help troubleshoot the issue.
If you can't send or receive messages on your iPhone, iPad, or iPod touch
Please don't hesitate to let us know if the steps resolved your issue or if you need additional assistance.
Thank you for using Apple Support Communities. Have a nice day.