Dear @Polyhandro,
Welcome to the Wefugees Community and thank you for sharing your question.
I am not too familiar with Belgian asylum procedures, but I am quite sure that you unfortunately will not be able to leave the country or travel during the pending asylum case without risking your asylum application. I am afraid that your partner either needs to come to Belgium or you need to wait until you are recognized as refugee/under international protection.
All the best,
Meike