This could be due to a few things:
- Something is blocking the connection between you and your bf. This could be a firewall, antivirus, bad internet connection, etc. Please make sure there's nothing like this causing it.
- There could be an issue with the authentication servers (run by GOG), that is used to connect all stardew PC multiplayer games. There is no definite way to solve this, but trying multiple times, signing in and out of steam, and even changing your steam username have all been reported to help.