Guy's dad and girlfriend were murdered and he goes back in time for revenge
Sounds like Gunslinger by The Scot his page is:
https://storiesonline.net/a/The_Scot
The direct link to the story is:
https://storiesonline.net/s/50644/gunslinger
You will probably enjoy the rest of his stories as well. I know I started with one and have read all of them.