Simply replace the unfilled areas such as "" and "[date]" with your information.
Dear [name of love interest],
It seems these days I can't bear to be around you without touching you. Whether our legs are brushing at the dinner table, or my side is crushed warmly against yours on the sofa while watching a movie, it is never close enough.
When we hold hands, my arm is jealous that my hand touches what it does not. When we kiss, my lips catch fire and sear away, and the pain when our lips parting is much more than the searing pain of their touch.
If not touching all of you at once is unbearable, then I can't imaging the pain of being without you, and hope that I never have to endure such a thing.