How to end a relationship?

How do I end a realtionship, ideally I'd like a separation before we officially end it, I think we have a chance but not without a break. The other party has no idea anything is wrong but for a long time I thought things were wrong. I want out, how do I not hurt the fella too much, basically. I've been agonising over how to phrase my break up and I can't do it. We now live seperately. I've been edging away, how do I make a clean break?