In all honesty, I feel having a love interest. /boyfriend girlfriend in the game would make it more interesting.
But I also believe that making the game multiplayer, you may just have more people buying the game because they can actually play with their friends and family and significant other. Yes, the game is great playing by yourself. But just think of the possibilities, you could have all those ideas you could put into the game if it's multiplayer, they could both have their own separate story that play into each other..