Understand the fear - gotta say the fear is usually worse than the reality.
Chances are you are not. HIV is not easy to get. I work with many LBGT and there are plenty of partnerships where one has it and the other doesn't inclusive of periods of time that they did not know and were having unprotected sex.
On the flip side if you happened to be the rare bird - it is best to know early and tackle it now rather than wait until your immune system has been affected. All that I know who are positive (with exception of one who found out last year) have been positive for 10 years plus and nobody would know. They are all very healthy.