or just used it too make it a katakana double vocal xD

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pardon me im being silly ;p

I just throw it there...might be a very stupid idea.
Chinese maybe? (but I don't speak the language at all).

First, OP said the bf studies Japanese. Second, I can speak a little Chinese, and it doesn't look Chinese to me. There's no verb, and to make the Chinese construction like "person for whom my heart blazes" the kanji would appear in a different order than they do in 心一人炎.

Well. I showed my boyfriend the translation KyleGoetz gave me yesterday evening.

He read it, but could not completely make out what it said. So I let him read the English meaning that I wrote on the back.

Then I asked him if he remembered what he wrote in my diary back in 2006.
He did and said he knew it was actually gibberish, but when I asked him if this is what he meant to say.. He just smiled and blinked at me.

I'm pretty sure it is what he was trying to say. I could see by the way he reacted and smiled.

A fun and nice happy ending. Thanks for sharing the story with us!

You're welcome, and thank you for helping me!

I showed him the translation while asking about the words he wrote in my diary and he got this look on his face that just said "oops, busted". :D

It was hilarious but also so sweet. He's way too shy to tell me something like that in my face.