First of all, it's not "Great For You" as in "Oh, well, good for you!", but rather as in "I'm so into you that I would be willing to do anything, and I need to be the greatest possible version of myself, because I must be great for you".
This song is a tribute to this indescribable feeling of longing for someone, in a positive and energetic way. From an emotional perspective, it's the famous cliché of knowing we both want each other but no one dares to say it.
The thing is that once the truth is revealed, there is no coming back from it; things will change. Funny how a truth, even an already-known one, can have such impact just because it has been told.
That being said, the song is not about saying it out loud: it's about feeling it, and about the things I've "Always Kept Inside" (that's my debut album name, by the way!). It's really the essence of the song and I think it represents the album perfectly, which is a gathering of the things I've always kept inside.