For now, concentrate on this S episode. Yuuichirou literally fell for Rei when he first saw her. (Inlove, that is.) But he was jealous of...Haruka? The episode starts with him watching her. She dreamt of the end, and was at a loss meditating, trying to figure out how to save the world. But the sacred fire almost burnt her hair, and he offered his band to tie her hair with.

Yuuichirou thought that Haruka was cheating on Rei. (He saw Haruka talking with Michiru.) We see later that he tried (as in just 'tried') to attack Haruka, telling Haruka to take care of Rei. Hurt, Yuuichirou left the shrine. We can also see Rei's sad face in the rain. She never stopped him when he left. She even calls him stupid, until Usagi tells her, that "Yuuichirou cares for you so much."

This isn't Yuuichirou's first act of chivalry, you know. He tried to save Rei twice. It would be sincerely funny to think that Yuuichirou would attack Haruka for Rei's sake (We all know that Haruka is just one of Rei's friends and fellow senshi). But then, he tried to block a huge snowball and Cooan's dark fire for her. Funny, maybe, as what his lovesick instincts would do. But despite that, watch this episode, and you also can't help but feel for him, because Yuuichirou's feelings for her were genuine.

Do you think Sailormars knows how much she cares for Yuuichirou? Let us put this way, she knows that the world is in danger with the Dark Messiah, and she even dreamt who she really is, but do you think she will admit this? See, in the end, she attacks the daimon "for my Yuuichirou." And later, we see Yuuichirou lying on her lap. (Rei tells him to apologize to Haruka for his mistake.) The last two silhouettes become close to each other. The last we saw Rei holding on to someone this close, was as far back as her dates with Mamoru.

It is probably the same in Usagi's case. Rei would not expressly admit it, but she cares so much. You just watch them both. Even notice the close-ups on Yuuichirou. He is handsome! And he was much more. Would Rei be dense as not to notice this? She knew that, too. Just look at them together!

Apatt has a nice and comprehensive page on Yuuichirou. You should see this, too!