It would seem pretty normal for Martha to react dramatically to the death of her son if she actually had a son. The thing is that George and Martha's son is purely "imaginary." When they found out they couldn't have kids, they solved the problem by just making a kid up. Even though he's imaginary, both George and Martha have deep attachment to the boy. Martha reveals the depth of her feeling when she says that he is, "the one light in all this hopeless…darkness". The darkness in question is probably her "sewer of a marriage," which she also describes as "vile" and "crushing". Burton is amazing.
This dream of a son seems to be so precious to both George and Martha because it's one of the few things they share. They created him together in order to escape from their "sick nights, and pathetic, stupid days". The boy is the one bit of real intimacy that the unhappy couple shares. When George "kills" the son it's like he dropped a nuclear bomb. Now George and Martha are left with no illusions behind which they can hide. By the end of the film, they must stare, unblinkingly, into the charred battlefield that is their lives. So, so sad. The film is amazing (even if it was shot as if it were strictly written for the stage, which it was. Nice random drunken camera 380 spins though). This film is a performance haven for these fine actors, and Taylor and Burton's real-life love for each other is so evident it glows. They seem oblivious to the camera, glued to one another and director Nichol's choice of shooting this movie in black + white only adds to these (truly) damaged individuals personal hells.
Oh well. Let's go grab another drink Martha. "Bourgen! see everybody, great things always come from great sufferings," proclaimed Jane.
"Let's now watch some Diane Bonder films and get this party started right. Cheers! A toast with a splash of Bye." mumbled the Unknown.