Context: One night me and my gf were driving at around 9pm when some random girl called me, I didn’t know who it was so I just gave the phone to my gf and she started talking to this girl. She hung up and later told me that it’s weird that some girl was calling me this late, and proceeded to say that I was cheating on her. I kept telling her I wasn’t and that I don’t even know who this girl even is. She told me that she didn’t trust me because it “all adds up. And that she lives close by.” I didn’t even know what she was talking about because we have been dating for two years, I understood that if some random guy called her late at night I would be a tiny bit uneasy but I tried everything to just explain that I don’t know who this person even is. I even asked around my friends if they knew who she was. My gf finally starts to believe me after about a day of me constantly telling her I don’t know who she is and that I’d help her find out who she even is.
About 2 weeks pass and the same girl dms my girlfriend and tells her that I cheated on her while she’s at work, my gf starts to talk to her, the random girl starts to say that I’ve been talking to her for our whole relationship and that I’ve cheated on my girlfriend with her. My gf then starts to come at me saying that I’ve cheated on her and showing me screenshots of what this girl said. I’m shocked when she first shows me because I have no clue what to say to her other than I didn’t cheat on her. I have no clue who this person even is and my gf says she doesn’t trust me and believes that I’ve cheated on her even though I’ve been with only her because I love her but she won’t believe me.
Any advice about how I can fix all this? Because I didn’t cheat on my girlfriend