Stuck on what if’s

About a month ago my boyfriend broke up with me and I’m having trouble moving forward. We dated for six months but it was different than any relationship I had, I loved him more than anything and I truly thought we would be together for a long time. He broke up with me because he decided he doesn’t love me anymore but now he’s acting different. He’s acting like a complete jerk, he immediately started flirting with other girls as soon as we broke up and he’s also been telling people lies about me. It’s so weird to see him that way because he used to really love me. He was a best friend to me and I still think about him all the time. He said he wanted to be with me forever but I think he just got bored. I can tell he’s hurt because he tries so hard to act like he doesn’t care. My question is, will he eventually realize that he made a mistake, or will he continue to be immature?