Thank you for trusting your question to JA today. I’m happy to be of assistance.
I first want to address a few issues concerning pay, so that you understand what is protected and what is not. Nothing in law requires an employer to give raises. There is also no requirement that every employee be treated the same. Comparing employees salaries is something an employer can certainly do, paying based on the "importance" of the position, but no sort of pay structure requirement is established in law. Essentially, an employer is free to make those pay decisions they see fit, fair or not.
What an employer is not allowed to do is make decisions based on certain protected factors, namely, race, religion, gender, age, disability or medical leave use. To make a decision concerning employment or pay, on any of those factors, would be illegal.
So, to the facts you specifically outlined, none are illegal in and of themselves. It is not illegal to fail to give someone a raise for 10 years, as raises aren't legally required. It is not illegal to give everyone but a single person a yes, in and of itself. It's not illegal to write nasty comments on a pay stub, in and of itself. It's not illegal to pay someone a very low rate of pay, provided that rate of pay is at least minimum wage. It's not illegal to pay someone a very low rate, even though that person has 20 years experience.
None of these facts, by themselves or even taken together are illegal UNLESS they are indications to support the position that you are being discriminated against based on your race, religion, gender, age, disability or FMLA use. From your stated facts, they appear to be more of an indication that the boss simply doesn't like you. While petty and unprofessional, that's not illegal.
So, I would look closely at your situation and think about any means of being able to argue that the actual basis for this treatment is race, religion, gender, age, disability or recent FMLA use. If you have any reasonable argument to that effect, you then have to consider the size of the employer because most discrimination laws don't apply to employers smaller than 15 employees.
If you have any further questions, please let me know. I invite follow up questions, so use REPLY for those. If you have no further questions then good luck going forward and please do not forget to rate my service with a top-three rating so that I receive credit for working with you today. Also, feel free to request me in the future, if you have questions concerning a different matter.