Just come out and tell her.
'It isn't that easy!'
Just open your mouth and say whatever comes to mind. Let your heart speak.
'My heart is beating out of my chest, I don't think it has time to speak.'
Just say something damn it!
"I, well, I..." He stumbled out some words, but he didn't know where to go. Finally, he got stuck on the only thing that made sense to him in the world, what with him being a major science geek. He started mumbling things. "Hydrogen... Helium... Lithium... Beryllium... Boron... Carbon... Nitrogen... Oxygen..." A large shadow hand came out of him and an audible sigh was heard before it smacked him across the back, bringing out a large breath of air, and. "IthinkIloveyouandIwanttoknowhowyoufeel!" He burst out, before panting, as if physically difficult for him to do so.