Why am I hurting over this?

Ok I just went through a breakup... i ended up having too get a restraining order and change my number. Well my ex keeps preceding with things. He found my new Instagram tonight and literally send me pictures of his ex and how he left the state too go see her for a month. Why does this hurt so bad? Like I’m in tears right now... i knew he would go too her eventually. He texted her while we were together last year. Does anyone have advice, or tips? Why am I so heart broken over this?