4 months pregnant and he tells me I mean nothing to him.

Ever since we found out i am pregnant, our relationship seems to be going more and more downhill.
I understand that I have been very emotional and snappy, I apologise for this every time I act like it but I seem to be unable to control my moods recently. I have tried to talk to my partner about how I'm feeling but he just doesn't seem to want to know... I watch other relationships who are going through the same and their partners seem to be very supportive. He told me this evening that he feels nothing for me any more and he doesn't want to be with me, he said he has felt this way for a long time even before the pregnancy... I don't know what to do, I feel so alone and pretty scared in all honesty. I thought I would spend the rest of my life with this man and be happy with our little family. We have been together 4.5 years and engaged 2 years. Why is he doing this now when I need him most?