This one is probably the best shonen with triangle love I ever seen. It's adorable, healthy, and so heart wrenching even I read it in one sitting. Well, it may not really shown the romance side that much, but once you get the scenes, it made you flutter with its cuteness.
I also love how the ending being potrayed. It gave us surprise. It leaves so many rooms open but it's good with its own way. It's like you're welcomed to imagine the possibility of the future they hold. I'm actually crying at the last (yeah) panel of this manga ugh. I'm glad I read it
Ao no Flag