Ideas for what to write in a love letter include the reason for writing the letter, favorite memories and a look toward the future. Since the letter is an expression of love by the writer, it doesn't have to follow any specific format.
Love letters often follow an informal version of a standard letter format, beginning with a salutation and ending with a closing. Common salutation options include "my darling" or "my dearest" followed by the recipient's name or a pet name the writer has for the recipient. Closing options include "love," "all my love" or "love always" followed by the writer's name or the recipient's pet name for the loved one.
If the letter is for a special date or a holiday, the writer can include a reference to that. Favorite memories are a way to express appreciation of the happy times the couple has spent together. A look toward the future reaffirms that the writer wants the relationship to last and strengthen.
Possible formats for a love letter include a list of reasons why the writer loves the recipient, a poem or a standard letter of any length. The writer can choose whatever format best suits the love letter.