Why would my boyfriend call me replaceable?

Anonymous
I don't think he meant it in the mean kind of way. We were talking on the phone and I can't remember how we got to this but he had said "You are irreplaceable... Well, actually, I can't promise you that you are." After that I didn't say anything for a while (cause I was feeling hurt), He added "If you died it would probably take me a year to get over you but then i'd have to find someone else. (pause, cause still, ow...) Please don't die."
I'm hurt that I was called replaceable. I mean, batteries are replaceable, people aren't. I'm not over reacting am I?
Why would my boyfriend call me replaceable?
4 Opinion