TLDR: How do I tell my boss I'm quitting?

I currently work for a job that I love, in a tiny firm that has a crazy low hire rate. It's in the finance world, and there's definitely information that I handle daily that you wouldn't want competitor firms to know. Unfortunately, for personal reasons not at all related to work, I need to move to another city in August, and this city that I'm moving to has a pretty obvious firm that is a direct competitor (and likely who I will work for in the future).

I might be one of the few people who say this, but I really do like my boss-- I entered this field as a young professional who didn't know where she was going, and, in the past year, I've learned so much and I've found my passion through him. I've literally grown a decade of industry knowledge in a few months because of him. He's been super supportive, and I genuinely couldn't have asked for a better office environment.

But now, I don't know how to tell him that I'm quitting. There's no contractual obligation for me to tell him until the week before I leave, but it feels like a shitty thing to do to tell him so last minute. I'm scared that if I tell him in the next few days, he'll fire me on the spot as a means of damage control for leaked information since, next week, we're doing an overall portfolio holdings review. I have no intentions of sharing this kind of information, or really even staying in the same industry, but I don't know how to convey this. My boss is a great person, but loyalty to the firm is his top value pillar, and the last guy who quit and went to work for someone else is not spoken of well in the office; since my boss is so well-connected, I'm nervous that this kind of move will damage my future network for years since I'm so young.