Break-up is bad no matter what you do, but you could always make it worst by not doing it the right way. There’s no way to break-up non painfully but you could aim for being neutral, non-accusatory, non-argumentative, empathetic & direct in your approach. You should be ready to face the consequences of break-up since you’re the one initiating the end of the relationship. There’s no need to delay the inevitable till the time they find it themselves and it’ll end up hurting them even more. So don’t drag it around, get it over as quickly as possible.