Emotional Rollercoaster

Sometimes I'm really excited to be having a baby and being a mom again..... But there are other times I'm thinking is this the right time am I ready for more responsibility.... I have a 5 year old and I'm currently expecting my second. I was 19 when I had my first child I'm 24 now. My first pregnancy was horrible I did it all alone no help from anyone! My first child after was never there and put me though so much. Its different with this baby the father is super involved and loves me beyond measure. I'm just feeling really emotional because im scared that if he were to suddenly disappear I wouldn't be able to handle it. Or is it just in my head...