no! when a man ejaculates, depending on many things, his sperm can be shot very far into your body, this is done usually to find an egg. The time of your sexual intercourse is irrelevant. Every male is different, so this doesn't help with anything.
nope. and any unprotected sex can involve varying amounts of sperm even if he doesn't ejaculate.
I don't think there is an absolute correlation. If a guy just doesn't have much semen on a given day (say he had ejaculated a few hours before), or if every bit of it shoots up into the uterus (maybe if the cervix is relaxed and open, the way it gets during ovulation), then you would not notice a lot of semen coming back out.
But you said that you DID notice a lot of fluid, so is what you are wondering how to tell if it was him or if it was just your own fluid? It seems a little odd that he would not know if he came -- most guys definitely notice climaxing. Also, usually the woman can feel the throb of a man ejaculating. If neither of you noticed that, it sounds like there is the possibility he didn't come.
If your concern is avoiding pregnancy and you think there is a chance he did come (is there a possibility he just thought you would kill him if he admitted he had?) then you might take Plan B if it is still within the suggested time period (72 hours, though the first 24 hours is best).
Sorry there is not a definitive answer to your question. I hope it all works out the way you want.