Very good advice posted by "achillea" - a similar though occurred to me when reading - she said it much better than I could have. Still, I'm a guy, so my support may add something.
Has a beta blocker been tried for the high heart rate?
I m so sorry you are going through such a mystifying and difficult situation. Clearly, you have a problem of diagnosis and treatment, and equally clearly, your significant other is having a hard time dealing with it all. Unfortunately, this is pretty common, and fairly often, this leads to a breakup.
My own feeling is that marital counseling can be tremendously important in these circumstances. Your own ill heath would appear to be the matter on tap, but the truth is that in any marriage stressed by illness, the 'well' partner can become exhausted and disillusioned if his/her needs as a normal person, not a health care professional, are not met.
Based on this fact, I would suggest that you and your man try one or two sessions with a family counselor to help everyone to understand what personal issues are at stake.
I know this does not address your particular medical concerns, but there is that other matter underlying it all, and it could be very important as you proceed to search for answers.