What does Tom's reaction to Myrtle's death say about how he felt about her?

Tom's immediate response, after learning what happened to Myrtle, speaking with her widower, and seeing her body, is to cry.  Nick says, as they are driving speedily away from the scene of the gruesome accident,

"In a little while I heard a low husky sob, and saw that the tears were overflowing down his face."  

This emotional response seems to indicate that Tom did, on some level, actually care for Myrtle.  However, he also blames Gatsby for the accident, believing that Gatsby was driving at the time it occurred, and so one might wonder if he's crying over what happened to Myrtle or if he's crying because he believes that this one man, Gatsby, has threatened to take away both his women in one afternoon: he might have succeeded in stealing Daisy away from Tom, and Tom believes that Gatsby has killed Myrtle.  Nick seems to believe, however, that Tom's tears really were for his mistress, as he tells Gatsby that "[Tom] won't touch [Daisy] [...].  He's not thinking about her."  He believes that Tom genuinely did care for Myrtle.