Got caught

So here's some background info on me

I'm 17 I'll be 18 in the beginning of December. I've been dating my boyfriend for over 9 months and he's actually perfect and we're so good together. I trust him with all my being. My mom got married last October and her husband is a control freak so I only got to see my bf maybe once a week for only 2 hours. So we started sneaking around and we eventually got to a point where I would go to my friends house and he would pick me up from there and I would sleep over.

Well my mom found out this morning and she's not mad but disappointed like she should be. We're going to talk to her tomorrow I believe and I just want some advice to help her understand why I made that choice to do that

Please no hate comments and shit. I love my mom dearly but she used to be cool before she got married to this guy and if he wasn't around my mom would honestly just let my bf sleep over and I wouldn't have to sneak around. Please just some advice on how to just open up and it not be some hateful comment