"I want to be the guy
You turn to when you're sad
That holds you when you cry"
-> "that" should be "who"

"But even more do I want to be the one
You trust with all your secrets
And that shares in your happy moments"
-> the last line does not need the "that". Should be "and share in your happy moments"

"Sadly I'm just some guy to you
Not the one you want around
You lead me to believe
I'm not good enough for you"
->Really powerful lines. Stood out for me.. until I read the last lines.

"'Cause just talking to you
Makes me feel like I'm not enough
And I can't take that feeling anymore
It's tearing me apart"
-> Great ending :)

It's a beautiful piece. Well-written!
Keep writing 5/5 :)

-X