Hey here's one for your destiel rec. It's not Cas stalking Dean, but Dean stalking Cas and holding him captive because he's convinced that Cas is his soulmate. It's really good and can get very unsettling because you never know exactly how right in the head either of them are or how reliable of a narrator Cas is. Nothing is black and white in this fic, you never know which side to take and it is very dubcon. It's a helluva ride though, and I personally loved that it had very grey morales. Give it a try if you are interested!

With Understanding by apokteino
http://archiveofourown.org/works/4907965/chapters/11258833