When he hits you with the ‘I miss you’ text

Soo my boyfriend and I broke up last week. We lived together with my son and I decided to move out, well at first he was acting all tough and like he didn’t care. He was calling me trash and a bad mom and a slut and terrible things. I’m going to be honest and say I said mean things back. So I completely moved out Saturday and he wanted nothing to do with me then saying bye every time we’d talk about the place. So now today I get a message from him saying ‘miss you, wish things didn’t go how they did.’ And of course I didn’t want to respond so I didn’t but deep down it’s killing me. I know we are no good for each other that’s why I left but it’s taking everything in me to not cave and message him because it’s comfortable. Help 😞