I wouldn't worry about your mum finding out, she's less likely to tell your mother than you are, due to the fact that your mum would be madder at HER than at her 19 year old son.
Cangratulations dude! God that sounds fucking awesome. So whenever you need to fuck you have somewhere to go. Lucky bastard.
This. This is something you would expect out of a 19 year old guy, not a 28 year old women who's a good friend. Trust me, she won't tell, if she does, then she's obviously stupid. Good job though