The problem

Using passphrases for SSH keys is a very good idea, but since UX is inherent part of security I would advise on adding your SSH key to the ssh-agent to prevent password re-type fatigue & mishaps.

The solution

Follow along the documents above or try this shortened version:

1. Add following line to your ~/.zshrc:

ssh-add --apple-use-keychain ~/.ssh/id_rsa 2> /dev/null

1. Add following lines to yours ~/.ssh/config:

Host *
    UseKeychain yes
    AddKeysToAgent yes
    IdentityFile ~/.ssh/id_rsa