There is no nice way to leave a relationship, how can one walk away?

My last relationship i just walked away, wasn't working out and she bored me. I told her i wanted my crappy shitty life back. I've just told my wife (fiancee) the same thing more or less. I can't keep on keeping on. I'm tired physically and mentally exhausted. My last relationship all i left was a dear Joanna letter. My fiancee deserves better, she knows i'm not happy. I'm OG from the estate we live in, shes an outsider from another country. She thinks she can handle it and i'm tired of reprimanding people for calling her yer English woman. I need to send her back to Britain, how do i do it?