Whens my conception date and what do i do about my man?

ok this one has been eating at me for a while ... heres the history ok, my man and i have been togeather for about 5years we have a son thats 2. for a while we split cause i couldnt take his jealousy and his controlling any longer so i got rid of him for a while... Then he came back and he had changed a great deal verry proud of him on that part.... but the thing is i was dateing another guy for a couple of months durring the break up. but there were a couple of times right before me and my sons father got back togeather that we had slept togeather while i was still dateing this other guy... about a month or two that we got back to geather i got pregnant agian ... yeah tell me abut it not the best thing but nothing to do about it now.... well my due date is origionally feb 3rd of 09 but since im haveing a c section its earilyer but lets just stick with the origonal .... so ok at first i was scared that it could be the other guys kid... but then i got to thinking about the dates and i know my sons father and i were togeather part of march and most of april .... and i stoped talking to the other guy way before april... so im damn shure that this baby is my sons fathers kid... but in the back of his mind he tells me that he thinks its not his... knowing this kills me but he knew and i knew the concequences that we were takeing when we were doing what we were doing he knew about the other guy... so if it happend to be this other guys kid wich im pretty shure its not ... my man is out .... but knowing this now makes me want to recoil and reconsider being with him because if he could be a man and know then ... why cant he be a man and take for what it is now? id rather do it bymyself now then do it later if thats the chance and for him to not show me affection b/c of the thought in the back of his mind makes me upset... so long story short whens my conceived date and should i stick with him even though he might be hesitant towards me? or should i just deal and stick around?