Welcome back to the forum.
The timing, short duration, and lack of certain other symptoms argue strongly that your fever was not due to ARS. Onset of ARS fever or other symptoms typically is 10-20 days after acquiring the virus; fever typically persists 10 days or more; and absence of sore throat (which you don't mention) and rash also argue against ARS. Recent research indicates that 70% of those with ARS have all three of those symptoms, and around 90% have at least two of them.
And a negative HIV antibody test at 4 weeks is at least 90% reliable. However, as the past partner of an HIV infected person, it would make sense for you to have additional testing to be 100% certain. You could have a duo test (i.e., the combo test for both HIV antibody and p24 antigen) at any time, or another antibody-only test 6-8 weeks after your last sex with your former partner; either of those results will be 100% reliable.
In case you have further questions about the reliability of HIV testing at various intervals, take a look at this thread from earlier today -- and the other threads whose links are in that one:
http://www.medhelp.org/posts/show/1449423
All things considered, it is extremely unlikely you have HIV. You can expect any additional tests to remain negative.
Best regards-- HHH, MD