Since at the time you didnt know and the deed has been done so to speak I wouldnt stress it. If you continue to see and have sex with him then you should disclose the information you have. I wouldnt bother expressing your concern about the other night and whether you passd it on because if you have - then you have and you can deal with it at that stage. I dont think it is morally wrong not to say anything now but it will just stress you out if you continue seeing him and dont say anything.
If he is going to show symptoms they will occur - most likely - within two weeks of the event and the most common time is within a week.