Boyfriend has space issues

So me and my boyfriend have been together for 6 months. In the beginning I let him pressure me into moving in with him too fast knowing that I wasn't ready. I needed space and felt overwhelmed so I left after Christmas. He complains everyday that we won't last because I'm not living with him, and always says that since I'm not living with him I'm going to find someone new and move on without him. He wants me to be with him constantly. I've never had a boyfriend who needed constant reassurances that I'm not cheating or talking to other guys. He has full access to my phone and I'm never talking to anyone when with him. What can I do to make him feel more comfortable with me not living under the same roof as him?