Ex comes back after 8 years then vanishes again! Why would she do that???

8 years ago i got together with my best friend who i thought i was going to marry then i moved away to complete my masters and she ended things..fast forward 8 years later and i moved back home for a job and started hanging out with my old friends how ever she is always around and keeps staring at me when ever she sees me out which is very uncomfortable..we eventually started saying hi to one another again and
unblocked eachother,then started to chat via text (mainly me) asking how her day was and to be safe..after we tried to be civil she would come up to me in parties and dance with me then walk away..recently i came to a party and ignored her presence because i was with some 1 else..she has since blocked me again because she said nothing has changed and doesnt want to speak to me again..my question is really why does she keep popping back by staring at me amd what should i do the next time i see her in our same circle of friends..another thing that amazes me is that every one else sees her as such an angel that does nothing wrong but i my eyes she keeps hurting me.whats up with her and why cant she stop hurting me