I just broke up with my boyfriend!! and the though of him being with another girl kills me what do i do?

I cant stop thinkin about it. . . I want to be with him but i have no choice cuz there is just so many things wrong and he doesnt respect me and is too immature. . . but the thought of him being with an another girl kills me inside, i start cryin and want to call him right away and try to talk and fix things for the billionth time. . . how do i stop thinkin this way?!?!