How do I write a letter of invite for my fiance in Nigeria?

First of all, what country are you from? The visa process varies from country to country. Is your fiance just coming as a tourist to visit you then return home, or for the purpose of marrying you and staying with you in your country? Again, there would be a different visa

There is no requirement for an invitation letter for most countries, You would normally need to apply for a fiance visa. If you are in the US, then YOU need to file a K1 is. If you are in the UK, then he needs to apply for one through the British High Commission

What do you want to invite your fiance to do? Go to a party? You need to say what you want! Do you want your fiance to visit you? In what country? America? If so, you do not need to "invite" your fiance. He/she just needs to apply for a tourist visa through the nearest American embassy...there is nothing you can do.

keep it simple and with your personality showing.

something goes like this;

hey, hunny..

i want to spend sometime with you, why don't you come over next week, you'll be my guest, what do you say?

hope to see you soon,

love.

i hope you have a wonderful time with your finacee.. best of luck