An unmarried partner visa states that you need to prove that you have been living together for two years. Also if your boyfriend is American then by marrying him you wouldn't have any right to stay in the country unless your boyfriend was a citizen. As you say a company will not sponsor you unless you are extremely qualified. The highly skilled migrant visa also comes with many points that you have to fulfil and this is generally almost impossible to do.

The only thing I can think is that you come back on a tourist visa on the waiver program but that means that you would not be able to access any work or anything so your boyfriend would have to support you.