I agree with Giga. Not being 110% upfront and honest isn't an option in this case. Put yourself in his shoes. He needs to know and its your obligation to tell him.
In some areas you can actually be criminally charged for not disclosing your disease history with partners, although I think its just AIDS so far but still.
So, so you think you can tell Heaven from Hell,
blue skies from pain.
Can you tell a green field from a cold steel rail?
A smile from a veil?
Do you think you can tell?
And did they get you to trade your heroes for ghosts?
Hot ashes for trees?
Hot air for a cool breeze?
Cold comfort for change?
And did you exchange a walk on part in the war for a lead role in a cage?