How do I move past feeling like “bust your windows” by Jazmine Sullivan?

I (28F) was dating Sam (27M) for about 4 months. He and I met at a community service event, he found me on social media a week later, DMed me, and things grew from there. He was doing all of the things that I was missing from my previous relationship and things that I didn’t know that I would like from a partner. He was very intentional and direct about wanting to be in a relationship with me, and he asked me after 2 months of casual dating to date exclusively. He ended up meeting my sister and friends, and everyone commented on how much he cared about me and seemed to really like me. I really liked him and was seeing a decent future with him. I have a 4 month timeline for dating, and said that if he didn’t ask me to be his girlfriend on Valentine’s Day I’d have to end the relationship. He told me that he had to go be with his family the night of Valentine’s Day and I did not get asked to be a girlfriend, so I told myself I would end things the next day. He texts me at 5am the next morning to tell me that he had actually been seeing someone else the whole time and chose them. I was heartbroken, not over not being chosen but over the fact that he had been lying to me. I actually told him early on that I was seeing someone else while we were casually dating, and he told me to my face that I was the only person he was seeing. We also had many conversations discussing how we felt about the direction of our relationship, all lead by him, and he never said anything. I have honestly never felt a pain like that before and I have been struggling not be reactive. I want to inflict a type of pain on him so that I’m not the only one hurting even though I know that isn’t right. I want to move past this anger and hurt but I don’t know how. If anyone has any advice I would greatly appreciate it.