My weird ex is pestering me?

it sounds like hes pissed about the break up, yet wants to irritate u by chilling wiht ur friends wihtout u and say awful things about u to them and the whole facebook junk is just another add on to his jealousy and anger towards you. i suggest you confront him to stop and if he cant respect that then get the authorities into the problem such as parents and even the police if it goes that far.