Most Helpful Girl
It really depends on the couple, but one person shouldn't have to carry the conversation all the time.
Most Helpful Guy
The more you contribute to a conversation the more interested and invested in it you are. There isn't an unwritten law for who is supposed to carry a conversation because that is how you judge the quality of the exchange. The closer to 50-50 the better. But yes always be prepared to carry the conversation until it becomes 50-50.