Were my rights violated when i was told i was not to work alongside my girlfriend at walmart?

I see nothing violating your rights. The employer gets to say what you do and what you don't do at work. The employer is not required to treat every employee equally. The law requires employers not to engage in unlawful discrimination, but I see nothing to suggest unlawful discrimination in what you say here. So the answer is, no, your rights are not being violated.

Not legal advice as I'm not licensed in Ohio, just my analysis of the facts you describe based on general principles of law. If you need legal advice, please consult a lawyer who holds Ohio licensure.