Your generosity knows no bounds! The photo is wonderful - I can imagine "Pa" on leave in his uniform visiting this location. Since I first wrote my post I have found that his Belgian friend's name is actually "A. Barrez", son of "A. Barrez-Lion" who was a glazier and picture framer in the Rue du Casino. Perhaps Pa met him whilst having a photo framed to send home to his sweetheart whom he later married (otherwise I wouldn't be here!). I'm now going to look at the map link again and see if I can find how Pa would have travelled from Jeumont to Brussels and back - does one do this journey by train?
You have been very kind and I hope to experience more of this "Brussels hospitality" when I arrive next week.