You have had accurate replies on the HIV community forum. Your test results are 100% reliable and prove you did not catch HIV. There are few if any medical conditions that alter the window period or other aspects of HIV test reliability, and certainly MS and its treatments do not do so. You should not have any more tests.
And if you want still more reassurance, why not talk with your partner and confirm he doesn't HIV? It is statistically unlikely he is infected -- but perhaps to reassure you he would be willing to be tested. If negative, you would know for sure you weren't exposed.
And please accept the following advice with the compassion with which it is intended. Your resistance to the repeated, reasoned, science-based reassurance you have had -- certainly on MedHelp and probably from your own doctor(s) -- is a sign of a potentially serious mental health condition. People with normal thought processes do not need such repeated reassurance. I suggest you talk with your doctor about this, and if s/he suggests professional mental health care, I hope you will accept that advice and follow through.
For more information about HIV test reliability, see the thread linked below, as well as the others linked in that thread:
http://www.medhelp.org/posts/show/1704700
Our experience on the forum shows that when persons are as inappropriately frightened as you are, ongoing discussion simply generates more "what if" or "did you really understand" questions. Trust me on this: there are no circumstances that you could possibly think of that would change my opinion or advice. Therefore, I won't respond. There won't be any follow-up discussion. This policy is in your interest.
Good luck with it all-- HHH, MD