According to the Comic Lois met Richard a full month after Superman left. Remember he's Perry's Nephew. He's also a damn good looking guy, can fly a plane and is pretty heroic in his own right. How could she not fall for him? She actually thought the Baby was born Pre-mature and that's why he's so sickly. Remember she has no recollection of being in a relationship with Superman and thought of Clark only as her Friend.