Thank you for your question.
I believe your assessment of his esteem is most likely accurate. it would be hard to know for sure without me talking to him to find out his side of things. BUT based on what you have said, that part seems accurate.
I do not thing however it is necessarily correct to say he is taking out his self esteem issues by making you work cheaply. I believe that is another issue based on issues related to boundaries and entitlement.
A lot of people, when in relationship, expect things of their loved ones, and close friends that they would never expect of a stranger. For some reason they feel entitled and have no problem mistreating those that they purport to love in the following ways:
1. Free or below market services for professional talents
2. free and low cost loans; and forgiven debt
3. special low cost deals at whole sale or less for products and services
4. not saying thank you or please
and so forth.
Using myself for an example: my sister borrowed 2,000 from my brother, but never paid him back. My girl friend expects me to work for her business and help her on her apartment complex for free, I even get taken advantage of as I actually ended up buying the products that went into her rental unit, for which she collects rent.
It happens with nearly everyone at some time in their lives.
Your boyfriend is taking advantage of you, but he is really taking advantage of the relationship, because of social issue related to boundaries and entitlement.
You are also part of that game. You accept it. You, at some point, agreed to do the work for that little bit of money. Like me, you did it because you loved him, and you wanted to be with him, and you wanted to help him. You did it, perhaps, because somehow you felt if you didn't, he would not want you or would not love you. (only you know if that is true).
Like me, you will have to make a decision. How is your self esteem? can you tell him, you refuse to work anymore for less than 12.50 cents an hour. Is your esteem strong enough that you can tell him, that you may be his girlfriend, but you deserve 12.50 an hour. AND are you strong enough to walk off the job if he does not give you the raise. Look in the mirror, and do a confidence check on your own self esteem and strength to stand up for yourself in this relationship. Do a list: what do you do for him over the past 5 years, and what has he done for you.
It does not look like he cares for you in the way you would like him to. This behavior does in fact sound like abuse in the form of neglect. BUT, you are letting him do it.
It sounds to me like you need to stand up for yourself and be prepared to walk. I would say you are abused, neglected, and under appreciated.