MacOS Sierra keychain keeps asking for the passphrase
Your id_rsa should be encrypted with a passphrase for security.
Then try adding it to the keychain ssh-add -K ~/.ssh/id_rsa
If your key is in another folder than ~/.ssh then substitute with the correct folder.
Keychain now knows your ssh key and, hopefully, all works now.
Also see this solution:
MacOS Sierra doesn’t seem to remember SSH keys between reboots