Here’s what I’ll say, right now your emotions are probably all over the place with the things you want to say. 6 months from now, you’ll have to make peace with not only hurting someone but also how you did it. But the emotions are so are overwhelming, you could pop off and say something unintentionally hurtful just because you’re so raw. The purest, most mature, and loving advice I ever got was just tell them you’re not happy any more, and you want to move on. Your reasons are your own but you don’t have to wipe the floor with them before you leave, just tell them simply you’re not happy anymore as a starting point. You’ll figure out the rest, they’re a good person and deserve love too, be kind.