Many things can make different sensations. Things to concider are lubrication (the wetter it is the looser it feels), how often you have sex (the more often you do it, the looser it gets), how hard his erection is (that can vary and obviously will make a difference), how far your cervix retracts (this happens the more excited you get), your position (some positions will spread the surrounding bones and tissue more then others), and also if you have used any adult toys that may have been larger then he is.

I would also be concerned that he is acting out because he is feeling guilty about something. Men have a tendency to play these reverse psychology games when they have been bad. You know, redirect the attention to you. Of course, none of us would know if that is the case, but it's something to concider.