I'm worried my girlfriend is gonna find out about my past

I have been with my girlfriend for 3 years. She is the most amazing person in my life and I love her so much. I never really told her about my past and I found out my mom is moving down to our city. We don't talk anymore. I'm worried my girlfriend is gonna find out about my past from my mom...

I ruined this women's life. I didn't mean to. I was a dumb kid and I moved so I wouldn't have to deal with it anymore. I was 15 and my mom had a friend who I thought was attractive. I even jacked off to her. I was a teenager. It was stupid. She came over to drop off the puppy her dog had. She was given us one. My mom wasn't home. I took the dog and she talked to me. I ended up telling her I thought she was hot. She laughed at first and said she was flattered and we talked. She said that I was very mature for my age and I have the maturity around someone her and my moms age. Long story short we had sex. We had sex for months and kind of a relationship but wasn't. I did really care for her and I didn't mean for things to go down the way they did.

My older sister found out when I let her used my phone and saw our sexual texts. Everything went to hell. Police got involved.. It was bad. My mom hated me because I ruined her friendship. Her friend spent I think about a year in jail. I found out from others her husband left her and she lost custody of her kids. I completely destroyed her life. Because with me she was left with nothing. A lot of people including her family where mad at me.

I know I fucked up and I feel guilty about it to this day. I know moving when I turned 18 was a coward move but my mom hated me and others had said I ruined her life. She was very well liked there. She was a friendly well known person. Its why my mom was such great friends with her. I hate myself for what I did. I should have just kept my hormones to myself. I don't want my girlfriend to hate me. I already hate me and have this guilt for years. Should I just tell her before my mom does? Idk if she will but with my old life moving here it won't be long before she finds out. I just think maybe it will be a little better of she heres it from me instead of someone else. I knew I would eventually reap what a sew and I guess that's now