It would not necessarily end up there. That depends on whether this Sou has a set of morals that get in the way of becoming a sex crazed bastard. Right now he's only gotten serious offers from his family, mostly Sumire. The other girls gave hints but none of them actually went and invited him actively. Sou is insecure in regards of how girls actually think of him and his main goal was to make friends and get a girlfriend, ideally... and then he also stated that he doesn't want to cross the line with his family since that would make him the R-18 bastard (not literally, but that's the gist of it).
The ultimate question is what would happen if one of the seven girls he had the most contact with came clear and would make a move on him - and I don't mean attacking him, just confessing that they like him that way. There's Miku, Kanaria and Hinata, either would get green lit. And Yuri, the only one he met completely alone at some point... currently she wouldn't do it, but if she went there, she'd be in the game. And now we can also add Aya, Hana and Kaede. I'd say either of them has a very good chance of achieving girlfriend rank, depending on how they go at it.
The first one who gives a damn about circumstances and responsibilities will have a huge advantage. If one of them asked Sou out, she would most likely succeed to be "First Wife" - unless her drill is not strong enough to pierce through Sou's density and/or he takes it as a joke.
From there onwards it depends on who that "First Wife" is and whether Sou maintains his morals (by being faithful to her).