How do I tell my parents I broke up with my gf?

Me and my girlfriend have been going out for almost 3 years now, and our relationship has been a bit rocky for a few months. We are both teenage girls, and she comes from a very strict and traditional family who want her to be with a Christian man one day. Because of that, we decided to keep our relationship on the down low.

I didn’t tell my parents, and she didn’t tell hers. We decided that we wanted privacy and that if we wanted to live together one day, we would tell our families then, but for now our relationship would be a secret.

But a week ago we broke up, and I’m still kind of heart broken about it. I feel super down and want someone to talk to, but I can’t. My parents don’t understand why I’m acting the way I am, and think I’m just being moody and sulking for no reason.
I want to tell my parents what happened to get it off my chest, but I’m scared they’ll be upset if they find I’ve been dating a girl for 3 years without their knowledge. My mum especially is not the most understanding and I feel like she’ll be furious- how can I tell my parents this??