But after having Chid and on her dealth bed she had admitted to the Duke of Fried that she had fallen in love with him. So maybe she isn't a responsible woman and falls in love with whomever comes along. That isn't what I think. If you were to be with some for a long time, Allen: few months and the Duke: few years, that it's very possible to fall in love with them.
We all know that she first saw Allen at a tournament where her uncle dragged her too. Also, we all know that she was staying in her room too much and that's why she was dragged to the tournament in the first place. So I think that if you stay in your room as much a Marlene had, you must've not had a large love life and had no interest in having one. But when she first layed her eyes on Allen she know that he was meant for her. That's what I call true love (sigh).
We all must agree that Millerna is the splitting image of Marlene and that is the reason why Allen had fallen for Millerna for a while. But once they go to Fried and Allen starts to think about Marlene he then starts driftng farther and farther away from Millerna.
Poor Allen was scent off to a fort on the Austurian and Fanelian border. King Aston was worried about Millerna and Allen's future relationship and had found out about Marlene's affair with him. So he quickly sends him away and keeps hatred against Allen.
I don't think that Millerna and Allen would have have worked out in the end anyways, and our poor Allen ends up being a bachelor at the end of the series.(where's a beam of light when you need one eh?)
both images are from " Never Giving Up".