Any advice to get through a break up?

So basically I was single for 4 years, from 17 to 21. And I hadn't feel a deep connection with anyone until I met this guy (this year). We hit it off really well and soon we started dating. Bare in mind, he just got out of a year long relationship just before we started talking.

I knew it wasn't a good idea to get together so fast but we did anyway. And I regret it so much. We got together within 2 weeks of knowing each other, everything just happened so fast and I started falling for him within a month. Actually I did, I thought he was perfect. And he was until the last month of our relationship.

We were only together for 4 months but we talked everyday we were always together and if we weren't together we'd be calling each other.

He suddenly broke up with me out of the blue. I didn't understand because I thought we were happy. He seemed happy to me. I know I was happy. But now I see him flirting around and it really hurts me.

I know 4 months isn't long but I really did give him a big piece of my heart. I feel so stupid because I just got myself together before I met him. Now I cry every night, I just really need some solid advice right now.
Any advice to get through a break up?
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