I have an ex who was very insecure and clingy. He was too insecure to break up with me in person or even by phone, so he did it by IM.
But then he wanted to be "friends" ... which basically meant him following me around like a little puppy, IM'ing me whenever I was logged in (which was a lot - CS major here), "accidentally" running into me on my way to class and trying to hug me, etc. I needed my space to heal and move on - he wouldn't leave me alone. Finally I had had enough and told him to just LEAVE ME THE F*** ALONE!! After that, he went to the opposite extreme - like he wouldn't get on an elevator if I was in it. I'm so much better off without him!