Like Nenad's you can't really miss anything. The story is linear apart from the choice incest or neighbour route. (Like Nenad's said just save there do 1 route first and then after you're done go back to the save and do the other route to get all the content.Is it possible to "miss" some content in this game? Like makeing wrong choices or something? Because i dont really want to play it with a walkthrough...
Having said that there's also a lot of content in the game that isn't part of the story. Open world stuff or referred to as unlockables in the walkthrough. Which you need to do various things to unlock.
Example collect rare coins that will unlock sex positions with a hot milf that collects them or unlocking a stripclub so you can do fun stuff with the girls inside.
Some of these things can be really hard to find/unlock without the walkthrough.
Can i ask why you don't want to use the walkthrough ?