Hi eljomom,
Thanks for being part of Apple Support Communities. We'd understand that you accidentally deleted a text thread and you'd like to try to recover those messages. We'd like to help.
Did you currently Use Messages in iCloud? If so, messages are sent to all devices as they are received. If you delete a message from one device, it's deleted from all devices. However, if you do not have that enabled, it's possible that some, or all, of the messages are backed up in iCloud or on a computer. Are you currently backing up your data to either iCloud or a computer? How to back up your iPhone, iPad, and iPod touch. If you do have a backup, you can try to restore your iPhone from that most recent backup to try to recover that text thread: Restore your iPhone, iPad, or iPod touch from a backup
If you do not have a backup, or are using Messages in iCloud, there is not a way to forward your current text thread from one device to another. You can copy and share messages within that thread but it will paste and send as one text message. This can be helpful if there are specific messages that you would like to have back rather than the entire thread. To do this, you would press and hold a message, and choose the More option. From there, click which messages you'd like and choose the Share arrow in the bottom right hand corner of your device. You will then be able to send those messages as a new text.
Hope that helps you start to build your message thread again with your friend.
Take care!