feeling weird about something

hey so my bf and i have been together for a while now but lately ive been feeling kinda weird like im not sure if its normal or what hes this super nice guy and we both agreed on no porn or anything but i keep having these thoughts you know? like i wonder how it would be with other people or stuff that might sound bad. im scared to talk about it even with him cus i dont wanna hurt his feelings. is this common?