I need advice: Length of a sex session?

I have been dating this guy for sometime now and the sex is great. He is larger than I am used to and he can go a lot longer than I have ever seen. My issue is I can have three to four orgasms and then my body has just had enough but he is just getting started. I don't want to disappoint him but I then do get dry. I do have KY that I can use I just also don't want him to think I am not enjoying him. I am just wondering what else if anything I may be able to do to help the situation.