I have over a hundred unread messages on my Apple iphone. I messaged one relative once, and since then have received messages every time they message each other. How do I get out of the message loop and how do I remove the messages from my iphone? Also, how can I set the iphone to not receive any messages?
A) Tell them to stop messaging you. You must be in a message group they have created.
B) On the “Messages” screen, swipe to the left to delete them all in one shot.
C) I don’t think you can, short of having your carrier turn off SMS.
You can click “details”’ on the top right of the message thread then “do not disturb” to not get notifications from the conversation.
But you’ll still get all those messages. Just tell them to stop! One of them needs to text the other directly as opposed to clicking on the conversation to send a new message. That will start a new thread - without you!
Thank you! 
Yes, you’re a victim of the similar and infamous ‘Reply to All’ email program syndrome that has caused much misery. The original sender sent the text with you as one member of a ‘text group’ and they have continued the text thread under that.
One nitpick: iPhones use both SMS and iMessage. SMS is for standard text messages, iMessage is only for iPhone to iPhone and merely counts toward your cell data usage (or nothing over WiFi) not your actual text messages count. You can tell the difference in the iPhone texting screen: SMS messages appear green, iMessages are blue. You can turn iMessage off but there’s no reason to, it won’t prevent the OP’s original problem.
I tried to delete them, but the only thing that happened was the unread messages, red, balloon disappeared. The message loop is still there.
The instructions **beowulff **gave must be done on the message ‘headers’ screen. That’s the first screen you get when you tap the green Messages icon from the Home screen. You swipe the entry with the name of the original sender to the left, then tap the red delete button (sometimes the iPhone will interpret a too short ‘swipe’ as a ‘tap’ and merely open the message thread again). You can’t do it from the actual message ‘body’ screen, the one where you read the actual text words in the balloons. If you tap and hold on the individual word balloons on that screen you can select & delete individual balloons if you want.
Step 1: Politely ask them to start a new conversation between the two of them because you are no longer a part of their discussion.
Step 2: Warn them that if they continue to include you in a conversation that you have no part of, you’ll have to block them and you will no longer receive messages from either.
Step 3: Block each person by tapping the “Details” button at the top of the screen, tapping the symbol to the side of each person’s name and/or number, then tapping “Block this caller” at the bottom of the menu (do this for each person).
I know it seems rude but at that point they’re practically spammers, treat them as such.