For the last nine months, I have been working at a small pizza business. I have been the senior crew member for a few months now. My manager hired my asst manager's girlfriend three months ago. Since then, she has become an asst manager as well.
Not to be bitter, but why would she get the position when she still has to ask me how to do simple tasks?
I already know that my general manager and the family of (both) my asst managers frequently spend time together outside of work... and I'm feeling the favoritism.
Does this seem wrong to anyone else?

What's wrong or not is determined by company policy.

Some have no restrictions... others prohibit dating or marrying coworkers. Many larger corparations or chain stors tend to have those but a privately owned business....less likely to have such a rule.

Since this isn't posted in a law forum....my opinion is its a really bad idea to allow it at all. I've personally seen too many major problems that happen....usually when the relationship goes bad.