Because it's not all official yet that you are a couple I wouldn't worry too much about it. If you want to make it official just sit down with him and talk over where you both see yourselves going. The best thing is to be honest with each other and talk all the time. If the moment is right tell him you have kissed this other lad and it didn't mean anything, tell him you just want to be honest.
Hope i've helped a little.
WaterDragon