He is probably wrong to have encouraged both Musgrove girls. But on the other hand, no one could think that he was seriously considering one particular girl while both were around him all the time. During their time in Lyme, Henrietta has been taken out of the picture and only Louisa remained as a possible candidate, at least to society's mind. I think part of FW's panic about the fall has to do with a little bit of guilt. He's been friendly enough with Louisa that she has felt comfortably being very friendly with him. While she was well, things could have gone one way or another. Now that she is quite ill, he has been put into a delicate situation. Does he stand back for the family to take charge as a mere acquaintance might? Some might see him in this light. Does he stand by Louisa's side as an 'intimate' friend (and possible fiance)? Others might see him in this light. I believe that he realizes this quickly after the fall and is quite stymied by the social entanglement in which he finds himself. As a captain on his own ship, he knows perfectly well his own place. But what is his place in this situation?