Chipa-san,
that's very romantic! So, basically you want to propose this lady in Japanese?
Let us help you
In Japanese, we usually say the most important thing at the end of the speech.
Accordingly, I'd change a bit of context order...
Dear (......),
...さんへ
You're so beautiful, I hope you will understand. I'm lonely and feels like want to be death. Since this is my problem. Don't know how to explain, I'll do my best to learn speaking in Japanese for you. It is not easy talking with you. I can’t wait to grow old with you, My love for you will never end.
[her name] さんはとてもきれいだと思います。
僕は孤独で、死んでしまいたいこともあります。でも、これは僕の問題。
どう説明していいかわかりませんが、[her name]さんのために、日本語を頑張って勉強します。
[her name]さんと話すのが簡単ではないからです。
一緒に年を重ねていきたいです。私の想いや愛情が消えることはありません。
Could you be my wife?
I want to be with you all the way, I want to make you happy, I'm waiting for the reply.
私の奥さんになってくれますか。
ずっと一緒にいて、[her name]さんを幸せにしたいんです。
お返事お待ちしています。
This is just a literal translation of what you wrote in English.
I have no idea about your current relationship with this person, so please understand that this cannot be the
best in any situation.
Are you currently studing Japanese? Does she understand English at all?
Sometimes, this kind of message can sound more romantic in English or other language
and, if you want, you can say only the most important part in Japanese.
Natsuko (奈津子),
Team JapanesePod101.com