Well there's a very similar premise like that.
He was adopted i think to a family and he fell inlove with his step-sister and same her to him.
But she got sick and died, it was curable but technology wasnt available then and it was already too late.
Along those lines, the Mc has photographic memory, he was successful and rich and he went back to the cave where they called their base or hideout or special place.
Got electrocuted via idk possibly lightning that hit and the cave was grounded.
He went back in time.
So his motivation was to advance technology to save her and or prevent her from getting sick in the first place.
He also helps his community to advance via job opportunities, quality education etc. etc.
It's time by john wales.