My cousin is about to tell my mum that I've been 'promiscuous with multiple people' help?

I'm 19 and I've had with 3 people. My cousin is 24 and is a virgin so she thinks she's a saint. My mum just had an argument with her about something completely irrelevant and so my cousin text me saying 'your mother's the one who has raised a daughter who thinks it's ok to be promiscuous with multiple people'. I told her this info about me in confidence and my mum thinks I'm a virgin. We're an Indian family so my mum will probably disown me if she finds this out. I think this is really mean my cousin is stabbing me in the back, what shall I do?