No, virtual worlds are not a game. You CAN play games IN them, but they, in and of themselves, are not a game. I choose to define virtual worlds as 3D social interaction platforms.
Firefox is a platform you use to access the Internet. A message board system is a platform for social interaction. Chat rooms are a platform for interaction.
Virtual worlds are whatever their residents make them, but at the same time, they are not pure fantasy, though roleplay fantasy can be enacted there. They are used and populated by real people who pilot various 3D avatars, so the interaction, the thoughts and the feelings are very real. Some build their dream homes. Some build roleplay sims and enact their favorite genre. Some use them to meet new people, friend and lover alike. Some use it as a platform for artistic endeavors. Yet others use them to explore themselves, their desires, problems, sexuality, etc.
Some use it for all and none of these reasons. The point I am trying to make is that you don't cease being human when you interact in a virtual world. The interaction part is as real and valid as if you were engaging in it with your neighbor down the street or a friend at a coffee shop. People DO fall in and out of love in virtual worlds. People DO forge and break friendships. You can't detach from yourself when you enter a virtual world, so what happens there on a human level is just as real, and as valid, as anywhere else. You may elect to keep your interaction with a certain person or people confined to a virtual world, but it doesn't make it less real. Things are possible between diverse individuals in virtual worlds that could never occur in the concrete, "meatspace" world.
I maintain that anyone who attempts to deny that feelings, thoughts, and dreams expressed in a virtual world are real is the type of person that looks at others throughout their lives and discounts their value in general.
Never forget that there is a fellow human being on the other side of that screen.