Well Josh619, if more HIV Negative people were like you finding out about sex with HIV Positive people (or as Bbucko correctly calls it serodiscordant relationships) there would be less 'surprises' for HIV negative people when they become HIV Positive 'Out of the Blue'
Now then back to basics before having sex with this man discuss with him they type of sex you want, understand your sexual preferences.
If the HIV man is a top, ensure that he has correctly fitting condoms, they come is selection of sizes, do not worry about asking him to show you which size condom he is going to put on his cock. In fact why don't you put it on his cock as part of foreplay then you would be assured that the condom was not too loose and going to slip off or too tight and going to split. It is also very good practice to change the condom every 20 minutes and hey guess what with all that stopping you last longer too - added bonus!
Still talking him as top, ensure that you have plenty of water based lube around and in your anus and that there is plenty of lube on the OUTSIDE of the condom (you would be amazed at the number of idiots who think lubing the cock and then putting on a condom is a good idea!!! - think about it.....) Needless to say there is a greater risk of HIV infection if his condom fails and he cums in your arse.
The infection risk also depends on his viral load (how much virus is in the body at that time). Viral load maybe low if his meds are working efficiently, but of course there are pockets of high concentration HIV in parts of his body. The viral load maybe out of control and very high.
NO ONE CAN TELL YOU THAT YOU WILL OR WILL NOT GET INFECTED WITH HIV WHATEVER THE VIRAL LOAD IF you have unprotected sex or the condom fails
We have all heard the stories that someone had sex with an HIV+ person and did not get HIV, THEY WERE LUCKY, VERY LUCKY.
Back to condoms, if you are the HIV Negative top, and the HIV+ person is the bottom, same rules apply, if your condom fails there is still a risk of HIV infection, HIV can enter your body via your urethrea or penis glans.
Unprotect Oral sex poses a few problems, the research suggests that unprotected sex is ok - and thank god for that, nothing worse than a plastic cock in the mouth!!! that said however, if you have gingervitis (bleeding gums) or mouth ulcers, sore throat or other damage to the mouth teeth or gums - yes teeth - what if you have just had one removed?? no oral sex until the hole is recovered and repaired.
Spit or swallow, your choice really, although personally, I prefer men I don't know to cum on the floor, bedcovers, tissue and not in my mouth. But if they do, I swallow because sometimes when I spit my teeth move (they're not false either) and I have had problems with bleeding gums
What to do in an emergency;
If the condom fails or you forgot to use one because you were drunk, get along to sexual health doctor straight away or to the Accident and Emergency and ask for PEP, PEPHIV, PEPSEHIV it's all the same thing
PEP = Post Exposure Prophylaxis (after exposure treatment)
PEPHIV = Post Exposure Prophylaxis to HIV
PEPSEHIV = Post Exposure Prophylaxis Sexual Exposure to HIV
These are anti-retroviral drugs that attempt to knock out HIV that you may have been exposed to, they must be commenced within 72 hours when they are about 40% effective but if commenced within the first couple of hours they are about 80% effective at stopping HIV infection. THEY ARE NOT TO BE USED ON A DAILY BASIS because you will build a resistance to them and should you ever become HIV+ there won't be any drugs available for you.
see
http://www.bashh.org/documents/58/58.pdf
Why not also take a look at the thread started by Tremaine
http://www.lpsg.org/193728-access-to-hiv-aids-treatment.html
Some HIV Positive men put pressure on HIV Negative men to have unprotected sex this is not a healthy relationship and best avoided, they heap on 'guilt' such as you don't love me because you won't have unprotected sex with me' walk away we are worth more than that.
I hope, that you and this man have a great relationship and a long and happy sex life
Brinz