He is building a bubble nest. It's where the eggs are laid.I recently bought 2 dwarf gourami (Don't know they are male of female) for my aquarium. I also have 2 Mollies, 2 Pleco. My Gourami has been behaving oddly today, swimming to the front and side of the tank and spitting bubbles hundreds of tiny bubbles through his gills at the bottom the tank every 15-20 seconds. I just wondered if you might have an explanation for why it might be doing this and what I can do if it something that should change for the happiness of the fish.
edit: So, perfectly natural behaviour, and nothing that you need to worry about as far as I know.