sex is pleasure of the flesh- earthly pleasure-(religiously speaking). when we die, our flesh is left behind. the soul is what lives on and it will be in new heavenly bodies. though is was created by God, sex is something that is for humans on earth. in heaven, we will have spiritual bodies. (i know it is hard for some of you guys to comprehend), but sex will be the last thing on your mind when you are in heaven..
i am unable to back this up with scripture at the moment. it is in the bible, i swear. (in more than one place, actually). i will try to find it later.