That being the case, it seems it could be a port-forwarding issue. Please make sure to open for both you and your partner the following ports in your router:
UDP 27000 to 27030, UDP 3478, 4379 and 4380
How to do so depends on the brand and model of your router. Here’s a general guide on how to do so but please bear in mind that it can vary wildly depending on the model: