I broke up with my boyfriend

I send a message to my ”boyfriend ” breaking up with him because he hasn't text me in 2 weeks honestly it for the best yesterday was my birthday (Sep 22)and I was hoping he would at least acknowledge me on my birthday but he didn't & he was the one who plans it so I kinda had a sad birthday, but I feel sad & release like I feel calm and not a crying mess, but I have a question how do you guy move on to a new relationship without having negative thoughts into your new relationship.