I'm so sorry to read about what your boyfriend is enduring. Nobody should have to live that way. One question here is whether his headaches are related to the cancer or if the timing was coincidental.
There are so many possibilities here that it's difficult to even know what type of information to share with you. Some of his symptoms correlate with Migraine symptoms, but of course, I can't diagnose or even hazard a guess regarding whether he's experiencing some form of Migraine. For descriptions of the various forms of Migraine and links to more information on them, please see Exploring and Understanding the Types of Migraine.
Among all the specialists he's seen, has he seen a Migraine and headache specialist? It's important to note that neurologists and neurosurgeons aren't necessarily Migraine and headache specialists. I've known many people to consult several different doctors, but only get the diagnosis and treatment they need when they finally get to a Migraine and headache specialist. You can find more information about these specialists as well as links to directories where you can search for one in our article, Why, How, and Where to Find a Migraine Specialist.
I sincerely hope this information is helpful and that your boyfriend gets answers soon. Please feel free to add responses here if there's other information I can assist you with. I'd also love to hear back from you about how both of you are doing.
with my best,