Really upset. I have to break up with my boyfriend.

I found out my boyfriend added his longtime ex on Facebook. When he wont even add me. He also follows her on Instagram and he blocked me off it. It's clear I have to break up with him and end things. But it's really hard. I don't know what to say or how to do it even. I just feel so useless and ugly. I didn't everything to keep him. I've never felt so hurt or betrayed in my life. It hurts because I would never do that to him. Any advice on how to get over him? And what to say?