As far as I know, the only difference is in how (some of) the scenes play out, more specifically the sex scenes. I think the actual overall story remains the same, but how you interact with the girls (or at least Natalie's daughters, and a couple other girls with their own separate choices I believe) will be different. I'm not sure if the actual sex scenes - i.e. the animations and whatnot - will be different, or if it's just the text, outside of the full route differences that are more obvious later on, which I'll avoid spoiling, but will be quite obvious when they come up.
What I will say, though, is that aside from a handful of choices, very few of the choices you make ultimately change things in the grand scheme of things. And to note, the choices you make in this game are not set in stone when you move on to the sequel, as it does not bring over your save from this game, but allows you to set your (relevant) choices again when starting the new game.
That being said, I've only ever played the "love" route, personally. So if anyone has actually played multiple routes can jump in to say if there are any significant differences between the routes, that would be appreciated.