These two are great to consider as parallels.
First, both want what they can't ever have. That which they both want happens to be attached. Although Gatsby wants Daisy and Myrtle wants Tom, Daisy's Catholic background prohibits a divorce. So a legitimate relationship for either pair is out of the question. Thus, Gatsby and Myrtle's continued faithfulness and devotion to their particular lovers will never get them the outcome they each are desperately searching for. The both travel on unattainable journeys.
Second, both look to materialism to fulfill their needs. This materialism is an avenue or tool to get to the relationship that they want to be in which, again, is unattainable.
In terms of career, neither have true careers. From our best guesses about Gatsby, we can read between the lines and assume he is indeed the bootlegger Tom pegs him to be. Myrtle, on the other hand, fulfills the role of a wife, but we don't even know how well of a home-maker she was because we only see the mistress in her character.
Each character is concerned with what others think of them and will go to great lengths to achieve approval.