A message that crashed my phone caused my message app to not open anymore and it just crashed

http://www.macrumors.com/2015/05/26/ios-bug-crashing-iphones-with-text-message/

the Solution 2 step:

1-put your iPhone date two month forward

2-go to settings > Messages >(under Message History, select keep messages 30 day)

NB: this will fix the problem but will delete all your messages inbox.

Hello scruffey,

Thanks for visiting the Apple Support Communities.

If the Messages app on your iPhone still quits unexpectedly after you received a message, the steps in this article can help:

If Messages quits unexpectedly after you get a text with a specific string of characters - Apple Support

Best Regards,

Jeremy