I feel like I am losing it!

I am 18 weeks pregnant and my husband told me today he wants a divorce. I met him in high school and married young. I didn't finish school and don't have my license. We have three kids together and I am scared. I know I need to stay calm for the baby but I am so heartbroken and upset. I wanted to be with him forever. We even bought a new house together this summer. I thought we had it all and now we are losing everything.