18 & Dating

So I'm 18 and I've been dating this guy for a year now basically. My mom is strict and doesn't want me dating but will let my brother do it. I told her about him over a month ago and she hated the idea and told me not to take him seriously. So, originally when I told her I told her we were dating since February. She got really mad that I wasn't honest with her. Although, from my perspective I didn't tell her bcos I knew she wouldn't let me date him in the first place and I wanted to show her I can handle school and a boyfriend. I ended up graduating with high honors & im going to a UC. How do I deal with a disapproving mother ? I haven't mentioned him around her since bcos she's never open to talk about it. Please advice!!!?? I've continued to sneak around even after telling her about him bcos she's that disapproving. He's not even a bad guy and she's never let me have the opportunity to open up about him.