I wanted to start off by saying that yes, lox and cream cheese is delicious! Haha.
But I agree that sex as the endgame is poorly handled. In the context of a videogame there's always some kind of objective or payoff you're working toward. Sex as the payoff for managing relationships makes sense, but it's not like everything ends once you jump in the same bed/cot/sleeping bag. The Jack example is pretty great because of how her character operates. But I wish that the ultimate act of physical intimacy could play the part of continuing the relationship, rather than some finish line at the end of it.
I suppose making it something you have to constantly maintain would be more accurate, but maybe more annoying. While not romance per-se, GTA 4 comes to mind as you have to constantly hang out with your friends or their familiarity level starts dropping or they get frustrated with you. Of course this wasn't helped by the limited activities or voice clips with people calling you up, so maybe a larger volume of writing or stuff to do with characters would help that.