I’m going to assume that you are working for a private (i.e. non-government) employer and that you are not a member of union that has a collective bargaining agreement with the employer. If those assumptions are correct, then in pretty much every state the employment relationship is “at will” meaning that the employer doesn’t need a good reason to fire you fire you. All that matters is that the reason for the termination is not among the few reasons prohibited by law. The prohibited reasons include firing you because:
- of your race, color, religion, sex, national origin, citizenship, age, disability, or genetic test information under federal law (some states/localities add a few more categories like sexual orientation);
- you make certain kinds of reports about the employer to the government or in limited circumstances to specified persons in the employing company itself (known as whistle-blower protection laws);
- you participate in union organizing activities;
- you use a right or benefit the law guarantees you (e.g. using leave under FMLA);
- you filed a bankruptcy petition;
- your pay was garnished by a single creditor; and
- you took time off work to attend jury duty (in most states).
The exact list of prohibited reasons will vary by state and locality.
You mentioned that the supervisor and Employee D were of the same race. It’s not clear whether you are alleging that the employer discriminates on race. Under federal law, if the employer has at least 15 employees, it is illegal to discriminate based on race. Most states also make it illegal for an employer to discriminate based on race and apply that law to even smaller employers than federal law does. Is there something that indicates race is the factor behind the differing treatment as opposed to something else, like personal friendship?
You also mention that you are openly gay. Here state and local law matters a lot. Federal law does not prohibit private employers from discriminating against employees based on sexual orientation. A few states and localities, however, do make that illegal. If your workplace is located in a state, county, or city that bars employers from discriminating against you because you are gay, then you may have something to pursue if you can demonstrate that the reason you are being treated differently is because you are gay rather than some other reason.

