Sylvia:
There are books of Napoleon's love letters available on
www.abebooks.co.uk
Formal letter writing in the 18th century could be very formulaic - there were certain stock phrases that you could bolt together almost like Meccano pieces. Most letters of formal condolence, for example, are very similar. In more private matters people seemed to find their own voice. It is interesting to compare Nelson's formal letters of condolence which were part of his job - they were kind, but brisk - we must all die....bow to God's will etc. with the letters of condolence expressing his personal grief, about Wilfred Collingwood and William Locker, for example which are much more emotional.
Personal letters vary enormously depending on the writer - some were amusing and gossipy, others more stilted and formal. Emma Hamilton's letters are full of her natural exuberance. If only Nelson hadn't destroyed her letters!
It is also interesting to compare Nelson's love letters to Fanny which were also full of formulaic expressions of esteem and regard with his much more dramatic declarations to Emma.