How to get over petty exes! ahh please please pleaseeeeeee help!?

ok soo me and my ex hugeeeeee history like had an on and off thing since 7th grade (we're in 10th now) and like we were eachothers first loves and yada yada and whatever but like nowwwww its over for good because he keeps doing really bad things to me and he just lies to me soo much! so i finally told him i didnt wanna talk to him anymore, and yesterday was his bday and i didnt even wish him happy birthday..and like ughh i miss him soo much but i just cant talk to him anymore! hes had wayyyyyyyy to many chances...and today i saw him little brother and it like almost made me cry..also his mom wants me to have his grandkids and i like love this boy more than anything but its just too late..and i miss him but i just cant even let him do what hes done to me..idk what to do! help!!