Some other things I missed in my last post that should return in a Romance Based Pack
The Love Tester Machine if your sim couples get the highest score on the machine it puts them in the mood for woohoo and it might happen. Also special moodlets we might get.
Heart Shaped Fireplaces were your sims can pull a chain on the fireplace and it lights up. These put your sims in the mood for woohoo and also produce a special moodlet.
Friends with Benefits Relationships meaning you can be romantic without falling in love if the two sims are friends or above. This however would cause jelousy if one of the sims were married and their spouse found out.