My girlfriend [F25] was messaging another guy, and I felt uncertain about how to handle it [M23].

I want to start by apologizing for my poor grammar; it’s not my strong suit! 😂 So, we've been together for three years, and yesterday was my girlfriend's birthday. I told her to wake up early and get ready because I had planned a special outing for her. However, I noticed she seemed a bit off throughout the day. Despite that, we had a nice time. When we got home, she told me she needed to share something important. She had been messaging someone she used to be more than friends with before we started dating. For the first year of our relationship, this guy would message her occasionally, and I expressed that it made me uncomfortable. She assured me she understood and promised not to contact him again. However, she reached out to him yesterday to say she still wanted to be friends, but nothing more. When she told me this, I felt heartbroken. I don’t understand why she would need to contact another man, especially since it makes me uncomfortable. This led to an argument that escalated, and she left. I couldn't just let her walk around at night, so I went to pick her up. When I got there, she kept apologizing for how she made me feel, saying she wasn't a good girlfriend. Now she’s asleep and won’t talk to me or eat anything. I know I love her, but I'm feeling lost about what to do. On a side note, she recently lost her job and has been struggling to find a new one. She also deals with mental health issues, so I wonder if any of this could be connected to what’s happening.