Okay thats strange. Problem solved, but it is strange. I never followed him, i had seem him all day since days in my activity (he is a follower of me) so I went on his profile minutes ago....and clicked "follow" because I did not know, what's or why it is happening...then i deleted him in my profile (he was the newest i followed because i clicked follow minutes ago.....yeah...). after i deleted him from there...my activity stream is okay again ö_- maybe theres something with my eyes, but if its okay, its okay now.