You can love two person at the same time. I do believe they both love each other. But they both know it will not end well. That's why when Aoi found his love AND place with Jirou, he begs Miyauchi to find it too. Miyauchi deserves happiness and not just suffering from the love and happiness that can't be delivered from him. Aoi loves Miyauchi, but that's all that he can do about it. He couldn't move mountains for Miyauchi just like how Miyauchi was always there to give him the best. It's pretty much a one-sided relationship.
Attachment, familarity, acknowledgement, and understanding almost always translate to love. Esp to people like Miyauchi and Aoi. So yes, without doubt, at one point, I do believe Aoi may had imagine spending his life happily by Miyauchi's side.
@abthurd and mtpvacal: Aoi and jirou both love each other since the beginning. They are each other's one true love. Don't forget that even when an option like miyauchi was opened, aoi still chose to be beside jirou despite knowing it will be painful. That is why I firmly believe that the love they felt is more about comradeship and attachment. Maybe lingering in between friendship and romantic but never more than that. Also, the confession Miyauchi made is nothing more than a provocation (which is half-meant I'm sure lol) in order for Aoi to be more honest with his heart.
In a way, I really think that Aoi really did love Miyauchi. A way that's different from an omega's bind to his destined alpha. I'm not sure hot clearly put it into words but I really do think that they did both love each other.