My boyfriend’s doubts

My boyfriend and I have been dating for 6 months and this week he told me he was having doubts about our relationship. He says his doubts are from insecurities because of his past relationship and how his ex hurt him deeply. I asked how can I help and be more reassuring, he told me and I’ve tried to reassure him but it wasn’t enough I guess. He thinks either of us can wake up tomorrow and feel like our relationship isn’t working out anymore (which is true but I’ve told him he shouldn’t think like that because we have no reason to leave and because of our history and how much we care for another). I’m confused about his doubts as I’ve tried to reassure I’m not his ex, but he has a wall that makes it hard for him to think otherwise. We both agreed to take a break for a week and see how he feels. I’m in love with this man and I don’t want to lose him because of previous damage from his ex that’s making him have doubts about me. What can I do? Please someone help I wanna cry.