How can I 21M open up to my girlfriend 24F?

techrat_2
A little about me, I work and study in College, along with practicing Mixed Martial Arts in my downtime. I'm purely a hobbyist and have aspirations to be an engineer. Anyways, I recently got a girlfriend before the pandemic kicked off. Things were great in the beginning. But lately my girlfriend has gotten mad at me because I don't confide in her about the things I've been through. I was bullied for a lack of a social ability things like having shoes thrown at me, being shoved into closets and lockers until I fought back. I've also got a strained relationship with my dad, and my mother was very abusive to my mom and brother. My brother got addicted to drugs and alcohol, while I moved in with friends.

I've had girlfriends but they ultimately cheated on me after I trusted them with this info on me. As a result I became avoidant when it came to talking about my folks, past relationships and upbringings. Overall, the only form of loyalty I've ever received was from my friends and instructor at the gym. When I've gotten into bar fights, they had my back. My past girlfriends always left when trouble ensued. Overall, I've explained to her why I struggle to confide in others outside of my MMA instructor and teammates. But I can't name anyone off the top of my head who's actually been there for me through rough times besides my training friends.

Any thoughts? I do feel like I'm falling in love with my girlfriend but at the same time, paid the price for getting too deep.
How can I 21M open up to my girlfriend 24F?
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