It is certainly implied that Luke, at least, has strong romantic feelings for Leia, and doesn't want Han competing for her affections:
Princess Leia Organa: [to Luke] Your friend [Han] is quite the mercenary. I wonder if he really cares about anything. Or anybody.
[she stalks out]
Luke Skywalker: [calling after her] I care.
Luke Skywalker: So, what do you think of her, Han?
Han Solo: I'm tryin' not to, kid.
Luke Skywalker: Good.
Han Solo: [baiting him] Still, she's got a lot of spirit. I don't know, whaddya think? You think a princess and a guy like me...
Luke Skywalker: [quickly] No.
And of course, Luke is very pleased with himself when Leia kisses him - just after the kiss, everything he does is intended to make Han jealous and demonstrate Luke's satisfaction with this apparent victory.
This shouldn't be all that surprising, since it is fairly clear that even George Lucas didn't "realize" (or "decide", if you prefer to call it that) that Luke and Leia where related until some point after the first draft of the script for The Empire Strikes Back was written and rejected.
From the books I've read to date, especially the original novelization of A New Hope, it seems that Leia thought Luke was sweet and cute, but she never really had any significant romantic feelings for him - she was just too focused on her instant love/hate feelings for Han. As we see in the movies, she is irresistibly attracted to Han, but she hated herself for being attracted to him, and it took a lot of effort for her to keep herself from showing her true feelings.
Luke was a nice guy - much nicer than Han - but he was also very naive, and he came across as much younger than he actually was and far less worldly and not at all the handsome bad-boy scoundrel that Han was.