I believe it was a full novel, that I must have read as a preteen, so it can't be newer than the late '90s or early 2000s. 

I don't remember much, but I think it was about a man who travels forward in time and gets stuck there, eventually falling in love with a tribal woman. He lives there for some time until they are going to be married, but then his time machine is fixed and he may go back home. I think the woman may also have been a princess or daughter of a chief or something. 

I could very well be getting some details wrong, and unfortunately I can't recall anything more clear than that.