The way I see it lately, it's not that Ike and Elincia never had a chance. He had a chance, she did seem to like him. He probably would have picked up on it, too. He just never pursued that opportunity. If a woman was dropping hints to him and he was in fact heterosexual (and did not hate her, which he obviously didn't), then he would either have gone the "moral" route and offered to marry her (since she's the queen and all) or been her lover at court. But he left court. He clearly isn't the type to just abandon someone he loves. (Mist follows him while he travels Tellius, and he takes Soren with him on that journey.) Thus I'm not convinced that Ike and Elincia were actually in a relationship.
Now, Lethe. Ike wouldn't care that she's a laguz, and he obviously does not mind the Branded and wouldn't hate having one for a child, so that's a nonissue. However, I don't see more than a (grudging at first) respect between the two. They become friends, sure, but I don't see any more in their relationship than between, say, Muarim and Zihark. They respect each other's strength and the racial differences are of no issue, and that's that.
What other women (or even men) does Ike have? As mentioned before, Titania is a mother figure. Reyson seems to just be guy friends with him (they talk about punching things, come on). Ranulf is his other tactician, and they do pair end, but they don't have as significant an emotional connection as Ike does with Soren. They didn't know each other as children. Ranulf was not near death, mute, and likely praying for a savior when Ike met him. It could be said that Soren owes his life to Ike--not just for feeding him when he was starving, but giving him something tangible to hope for, to put a face to that light at the end of the tunnel so he can have something definite to search for. It's possible Soren may be confusing overwhelming gratitude with love, as he's never felt love before, but that doesn't account for his unusual emotional openness. With the way he's been treated, he's got to trust someone very deeply to open up like that (and Ike's a very trustable guy judging by all the random people he recruits), and as we all should know, real relationships are built upon the openness and trust that both of them show in that extra scene.
mm, just my musings at the moment