Yeah, blue gouramis get too big for a 10g...so you'll eventually have to upgrade. And they can be aggressive.
If both gouramis are male, I'd take one back to the LFS...well really, I'd take both back and get a dwarf gourami and some neons or another small school of tetras.
My blue gourami is about 4 inches now...and the ruler of my 29g tank.