Why am I doing this? What is wrong with me?

My ex and i just broke up..Terrible relationship. I love him very much but it was an unhealthy relationship. It lasted 3 years in which midway into it he told me he was married with 2 kids. I stood with him like an idiot.I was willing and did anything for him but it wasnt the same for me.Anyway, we parted ways finally a couple of days ago. i told him to give meback the sim card to our family plan. I checked the voicemail and found his ex from like 5 years ago on it leaving those "sweetheart "kinds of messages to him. I suspected he had something with her but he said she was just a friend which I think proves he was lying once again. This isnt even his wife which he is stil with!Now i cant stop calling her and hanging up on her like a stalker. It's like an impluse.I want to curse her out .im digusted with her because she knows he is married but then i feel disgused with myself because she is no different from me.Still i feel like i hate her and i cant stop calling Why am i doing this?