Concatenate / Combine values based on another column

Kia Ora

I would like to know if there is a way of achieving the following: I have a table that has codes and a key that identifies related codes. In the example below all one's are related, all the two's and so on.

I need an output that combines the codes when they are related by a key - see the desired outcome column.

As seen in the example below there can be multiple codes that are the same for the key. I just need a combined outcome of each distinct code for each key.

I also need the outcome to shoew in the same format for each row. i.e. for key one each row must be ABC123 / BCD234 and not a mix of ABC123 / BCD234 & BCD234 / ABC123.

I would eb very gratful if anyone know if this is possible.