What is this feeling? What do I do?

A few years ago I was in a relatively happy relationship. One night he spoke about god and life and the future and suddenly I felt anxious and uncomfortable. That feeling stayed and even being touched by him made me want to shrivel away from him. I ended up breaking up with him the next day because I couldn’t handle the stress of that feeling. 

Years into the future I am with someone that I have been very happy with for three months now. He mentioned the lack of sex lately and that he thinks it’ll be an issue in the future. We had a conversation and suddenly I once again feel uncomfortable, scared, almost sick. I feel panicky and anxious. I feel like I need to distance myself from him but I don’t want to because I know that’ll strain our relationship. I want this relationship. Not at this exact moment because I am uncomfortable, but I know I don’t want to lose him. I am so stressed out and I have never found anything that explains what I am feeling, what this is. I don’t want to feel this way anymore. I want to be able to cope healthily and move past this.