I’m confused

So I am currently dating a guy for the first time in 2 years. He is very sweet, respectful, nice, and pretty much everything a girl can ask for. At first I liked him and you know, I thought things were great, but lately I haven’t been feeling anything for him. For example, I don’t get butterflies when I see him or hear from him, I just feel numb. I just don’t know what to do. I don’t want to lead him on but I don’t know how to let him down easy. I feel like a horrible person.