I read this book from the mid to late 90s.
There were humans on Earth but these two specific humans were from another planet. They were lovers from a long time ago, possibly thousands of years ago. They would lose each other periodically and then find each other again.
I think the time was set in current times but they were together in Egyptian times (they may have ruled together?) as well.
He dies then and he dies in the current time as well (I think) I'm not sure if they are reborn or what. These creatures are human but they somehow live a very long time and have seen a lot. It might be a love story.