Freaking out over Finances!!

I’m 16 weeks, due in April. My fiancé wants me to stay home once the baby comes. I don’t have a degree or anything, I work a regular sales job 40 hours a week and I’ve been working since I was 16, independent paying for everything myself. How do I transition into a 1 person income with a baby!!!! Obviously I can cut back my venti iced coffees on the weekends and shopping all the time, but I’m freaking out. I know in the end it’s my choice if I go back to work or not. I would love to stay home with my babe everyday, how do I get into this mindset? Help :( any moms that stay at home been through this???