To know who sent a message, the senders need to sign their messages.
To add your signature, click at the bottom right of the screen (pink arrow) and write your name (or a sweet nickname). Now the signature will be applied to all your future messages. 👍
Warning: you have to add a signature for each Lovebox you want to send a message to. You can sign "Mom" for the Home Lovebox, and "Sabrina" (if Sabrina is your name) for your friend's Lovebox. ✍️