What Jaheim has recommended there is the best thing,talk with the chap as a matter of urgency and get tested at a VCT,he may also be eager to know. If both negative,youre home free. If not/unable to continue as below:
As far as i recall PEP is effective up to 72hours (3days) after exposure,however you need to be sure that you have not been a HIV carrier longer than the 72 hour period since you could get your immune system compromised and have an early onset of AIDS and in consequence,quick demise. It is also quite expensive if you are paying for it yourself.
If you have little money,you may not even need to take PEP,if the test at VCT is negative and you do not want to commence PEP,go to KEMRI and ask them to screen your blood sample with a PCR machine for HIV. This is an extremely sensitive test (can detect minutes after entry of virus) and will tell you whether there are any viruses at all in your body and if they are enough to form a viable innoculum ( dose of viruses to cause infection) it will cost you kidu 6K and may save you the hustles and cost of PEP. This type of screening is what ensures pornography actors in some developed countries never get infected despite all the unprotected sex they have. The VCT test kit is designed to check for antibodies which may take up to 6months to develop and therefore has a window for error in your case.
ANECDOTE
I sympathize with your situation,i was once the type of man to 'fear' a few years ago in such a case,however the reputation was unnecessary as i always used protection.One time,i met the most charming,hottest,cutest,innocent lady who fell for me. One day managed to get her into my bed and i for the first time did not want to use a 'tube ya baiskeli'/condom at all. At the time we had both stripped and i could not believe this angel was asking me to put on a 'tube ya baiskeli',for some reason i knew her status,(hint: we worked together) and i was guessing mine. So she covered the socket with her hand and asked me 'you want to give me you diseases?',i put on the tube and we went VCT the next day.
Niône mwisho ya mwezi pliz!
Meru Holiness