Heero Yuy. Relena Peacecraft. It is true, that in the show, Relena follows Heero around like some kind of lap-dog. It is true, in Endless Waltz, Duo believes Heero has 'a crush' (original subtitles from Japanese version). And yes, so he can't kill her. However. Yes, this is my however. He doesn't at any point express great love for her. Neither does he express great hatred for her. Just... well, he puts up with her. She follows him around, and he tells her he'll kill her, but it's all empty threats. 

Maybe they could get together. Maybe. But this is my site, and in my opinion, Heero and some one else belong together. Not Heero and her. However, I don't deny that it's possible. You'd have to be blind not to see that Relena cares for him quite a lot. Even if only because she's a nosy old... *pauses* ok, I'm going to leave it at this. yes it's possible, but in my opinion, highly unlikely. And I don't like her much. She belongs with someone else too.