Girlfriend of 5 years cheated on me

So I dated this girl for 5 years. Her family is trash and so my family and I kinda took her in. We gave her a place to stay, a job, took her on trips. I was the best man and the best version of myself I could’ve ever been for this girl. My family also treated her like our own. We also have a dog together. We had a beautiful relationship, no problems whatsoever, we were very happy.
Anyway, with my help, she got into the same school I did (a good school) and then again with my help, she found an internship. Fast forward, she became friends with her managers son that is also an intern at the company. The guy made me a little sus and I told her multiple times that I don’t like it. She kind of ignored me about this, started a streak on Snapchat with him which I then told her that I’m not okay with it. She kept snapping this guy even though she told me she had stopped. One day I told her, let me see if you stopped snapping him, and she goes “do you not trust me?” I went to their chat and it was a lot worse than I thought. They had been messaging like they were dating, calling eachother baby, telling eachother I love you, etc. she told me that she was scared to not continue it because he’s her boss’s son and so I told her that I’ll give her the benefit of the doubt and I was willing to work through it. But then that whole week she kept ignoring my texts, and told me she needed a break to “find herself”. Then at the end of the week I told her that I’m done waiting and that we’re either working through it or we’re not. She ended up breaking up with me because she “needed to be single because she lost herself and doesn’t want to be in a relationship”
Ever since then, this girl has been acting like a complete asshole towards me, acting like I’m the one that hurt her. She started dating the guy pretty quickly. I even found a picture of him holding her that was taken a day before we officially broke up. It hasn’t even been a month and the guy already met her whole family.

I know I deserve better, this girl is probably a narcissist and can’t sit alone with her regret and sadness so she had to quickly find her next victim. But this all just sucks. I loved this girl so much, I planned on proposing this year, we had our whole future planned out, we had 2 apartments together. I got into many fights with my family due to her, always protecting her, always avoiding seeing her bad side. But I guess it’s my fault, her family is truly the worst, while mine is amazing.

I don’t know what to do, all I do is think about that asshole, that girl that completely betrayed me, the girl that does not care how much I’m hurting, as long as she’s happy.

One last thing I’ll mention is that this guy is HIDEOUS, and I’m a good looking guy, but I guess this guy has money? I guess she likes that his dad is her boss?

She doesn’t get on Reddit but if you do, fuck you, you’re a complete asshole, you’re a horrible person, you have a terrible heart. I always thought you didn’t belong in your family but you do. You’re probably the worst of them all. I poured my heart out to you, I gave you my everything and more and this is how you thank me. You will never ever see our dog again. I hope it was all worth it, you horrible, disgusting human being.