How to move on after losing the love of your life?

I (31M) am going through a very rough time. A little over a year ago, my life fell apart. My girlfriend (who is now 25) suddenly broke up with me after a 5-year relationship. We met in college, but I had to drop out due to financial issues. For her, money was never an obstacle; she supported me financially without ever questioning me and loved me truly for who I was.
We had a long-distance relationship (about an hour away). She always made the effort to come see me, never demanded a cent, and never pressured me about work. Eventually, she started worrying about my future and pushed me to enroll in a technical school so I could have better career prospects. She even bought me my uniform.

The last year of our relationship was very turbulent due to the distance. I made the worst mistake of my life: I cheated on her with a girl I met at said school. She found out because the other woman messaged her on social media. Instead of leaving me right then, she suggested we open the relationship. I hesitated because I didn't want to "share" her, but I ultimately agreed because I was terrified of losing her.

She immediately started seeing an old flame, and our intimacy completely died. I felt miserable and eventually asked her to close the relationship again, but she told me she’d rather just break up. I was in a very dark place mentally, and since she was my only friend and confidant, she agreed to stay and close the relationship for a while longer. However, she became a ghost. She didn't invite me to her graduation, stopped telling me things, and didn't visit me for three months. On December 1st, 2024, she broke up with me over the phone out of nowhere. When I tried to reach out a few days later, a man I didn't recognize sent me an audio note telling me never to contact her again.

That hit me harder than anything. I’ve tried to get back out there and meet new people, but I feel incredibly disillusioned. It feels like every woman I meet now is extremely transactional or only interested in what I can pay for… something she never cared about. I feel alone, I’ve lost my ability to trust, and I’m exhausted. I feel like I lost the only person who truly understood me, and even though I know the relationship became toxic, it feels like everyone else is worse.

I know I messed up big time, but the void she left is massive. Any tips on how to handle the guilt and how to start trusting people again when you feel like you've already lost the one?