The spelling of "fayne" might seem unusual, but it actually follows English language phonetic rules. In IPA phonetic transcription, "fayne" is pronounced as /feɪn/. This indicates that the word has the diphthong "ay" which is a combination of the /e/ sound as in "bed" and the /ɪ/ sound as in "pit". The "n" at the end serves to indicate a nasal sound. So while it may look odd, "fayne" is actually a valid spelling for a word pronounced as /feɪn/.
The word "fayne" has its origins in Old English. It comes from the Old English word "fægn", which means "happy" or "glad". Over time, this word evolved into the Middle English "fayn" or "fayne", both retaining the general meaning of "glad" or "pleased". It has been used in various contexts throughout history, including in literature and poetry, to express happiness, contentment, or willingness.