You can play all 3 without restarting the game, but they have different objectives.
Story path: It will be only content that helps to advance the plot of the game. If you finish one of the Story Paths, you reach one of the endings of the game, for now there are 7 ways to do this. If you advance more than one in parallel, the ending also changes, but the minimum requirement to reach the end is to finish the whole story of only one of the main girls. there are tons of ramifications so to long to explain lol
Love path: Will be the content focused on forming a love relationship with one of the girls, representing the trust and relationship between the player and the girl. This unlocks new interactions and extra content, focused on more wholesome things xD
Depravity path: It will be the content focused on the sexual and explore different fetishes, each girl will have some specific ones, the more points in this path, the more extreme things they will be able to do. For example, being dominant with Maxy, threesomes if two girls have enough depravity points, etc...
if you just want to finish the story, you advance the Story Path, if you want sexual content, you play the Depravity path and for bond the Love path. If you want, you play a bit of everything, or ignore the story completely, idk, the idea is to give more freedom to the player to do what he wants when he wants
I think I'll make a post on Patreon explaining everything in depth xD