The reason Aileen and Roy work for a while and then stop working so hard is because at first Roy kind of saw Aileen as this very stable, responsible, perfect choice, and at first Aileen kind of sees Roy as this exciting, romantic, very fairytale kind of love, and obviously these ideas come crashing down, because Roy is very far from a knight in shining armour, and even though Aileen is very responsible it is in a "superhero team leader" way, not a "settling down" way. So things start falling apart early and then slowly unravel, but still with their sweet moments that make them keep holding on. And what would they do without eachother, and what they're going to split up they work together. And then during "world's collide" their ideas of eachother come crashing down around them, and there's nothing left for Aileen to do but leave.