If your boyfriend is working and has health benefits, he can add you as his dependent. Thats the best option.
Some companies allow significant others/domestic partners to be added, even though they are not married. That would be a cheaper option.
You can get insurance on your own from any insurance company, but the premiums may be high.
Some states do have low income programs, that you could qualify for, but make sure you do not have to be a PR or citizen for it. Some states also have clinics, that charge very minimum or free for walkin services. So, at least you could get some basic care. You should not apply to get any benefit from US government such as Medicaid because when the time comes to fill out for GC paperwork and interview, you may have to prove that you were not dependent on US govt.