toxic relationship ended....

me and my ex were together for 3 years before shit hit the fan and got bad. around the 2 year mark he would start to disappear for months or weeks at a time. that really got to me cause i wanted to marry that guy and be with him. then around the summer of 2016 i think he wanted me to come see him i wanted the same. we talked about times, airlines, finaces and planned it. then august cam around for our 3 year and i never heard from him. thrn weeks went by i didn't hear anything. i messaged him non stop and then months later still nothing. so i broke it off over text since no from of communication worked. then after that the lack of closure got to me and i was wondering what the hell happened. if it wss some guy i knew for a month i wouldn't think anything of it, but it was my high school sweetheart who i wanted a future with. to this day ive moved on but i still want to know why he did it and why he thiught cutting off communication was best.