HELPPP!!!

OKAY here my story, my ex boyfriend logged into his imessages on my Iphone but since that happened all the apps that he has and i also have such like twitter, instagram, facebook, tumblr it logs in as me so he sees eveything of mine and he logs out but if i happen to log out on my phone and log back in, it automaticlly logs me in on his phone and i want this to STOP! Also my contacts and calander notifications pop up on his phone and when he deletes the contacts it deletes from my phone as well. help!!!! or is my best bet just to go up to sprint or can i do it from my phone?