What phrases can you use to express how it hurt you to break up with someone you love after hurting you?

Tough question but I always go with honesty--tell them that it's not possible for you to be with someone who could make you feel this way but you're glad to have had the chance to have met him or her and that you enjoyed the good times you shared. Wish them all the best and then go. Do not wait for apologies or something that will get you to change your mind, because it will likely happen again and you don't need that.