Hi Katie,
This is really good. I can understand what you're feeling. It makes sense and it wouldn't be hard to find the melody.
I've put on my prettiest dress
but it wasn't his eyes it was mine
now I can see, what makes him happy
it isn't the sea , or the wind in his hair
It's me being there by his side
I'd be more satisfied if instead of "now I can see what makes him happy" you wrote "now I can see what makes me happy". It seems to me her dedication to him even though he may not return her love is true love, and if she realizes that loving him is as important as being loved by him, she'll come to terms with their situation and find happiness.
But that's just an idea. It's lovely the way you wrote it, too.
Lynn