I think that description of the sleeping arrangements tells us two things we didn't know before. Firstly, that Achilleus has found a replacement for Briseis and secondly, that Patroklos has at least one concubine.
This is Homer's euphemistic way of telling us that their sexual needs are being met by women.
I am sure it would have gone over more gracefully in a poem than just saying outright, "Oh and by the way, these two weren't lovers"

