Idk what to say to my boss.

Okay y’all. I need advice. I currently work at a hospital and I’ve been there for over a year. I used to love this job but ever since a few things changed I can’t stand the job. I dread it everyday. I’ve walked out once but I got talked into coming back. Well I found a new job and had an interview today. He was going to hire me in the spot but said that I need to talk to my current boss about scheduling because he doesn’t want to schedule me and I can’t make it in. I am keeping my current job for now just to see if I like the new one or not. That way I don’t quit my current job and hate the new one and have no job at all. He said the scheduling around my new job shouldn’t be a problem he just wants me to let my current boss know so I can get ours at the new one to. The newer one pays more and pays weekly which I need because getting paid every two weeks is a struggle. The new job also has hours that I could have if I wanted to go to school in the fall instead of the current job I have. I’m pretty positive if I like this new job I’ll end up putting my two weeks notice in. The reason I’m here is because I don’t know what to say to my current boss without her getting mad. We’ve gotten into it before and she gets mad easily. My husband works with me and I asked him what he thinks and he told me he’s afraid if I tell my boss I got a second job she’s going to find every way to make it hard on me and be mean to me. I told him I’d walk out if so. But right now I’m just wanting to tell her that I have a 2nd job and I need to have a set schedule. Even though the second job would be on days that I’m off with my current job. And on days after my job. It wouldn’t be a problem. I just know she’s going to have some reaction. My boss is getting ready to go out for surgery and I’m a little nervous if I do quit because then she’s going to be way short staffed. But my happiness is way more important then a job,you know? What do I say? Or how do I approach her?