My girlfriend cheated on me. What do I do now?

I am a 19 (almost 20)-year-old man, and I found out that my girlfriend is cheating on me with another guy. My girlfriend (or ex) is very busy with her campus organization, and ever since I found out, she has been disrespectful towards me, rarely responding to my messages. Her friend messaged me, saying that my girlfriend is cheating on me with another guy, and they even sent me a photo of my girlfriend with the other guy together.

My heart is shattered. I've tried my best for her. We've been in a relationship for 18 months (last 6 LDR), and I love her so much, but she's just..

My heart is very broken, I can't find the words to say...everything feels like an illusion now. I just really wished I could love her still but it's best to break things off.

I love her so much, but damn, I'm so disappointed and angry. I don't know if I ever want to find another relationship again after seeing this stuff happen all the time. I had my childhood be exposed to infidelity and I always hoped that this would never happen to me, and sadly it has. I just really wish I could find a decent woman in person and even online if I have to, to date and maybe marry that is loyal. Just seems like 1 good person in a million in this generation based on social media atp.