I think that its more of a problem that Deadpool and Elektra have never had any kind of relationship themselves, so there is no substance to Deadpools jealousy.

This takes Deadpool out of his usual ball-park of 'funny, crazy', and puts him firmly into the ball-part of 'just crazy'.

Its the kind of sinister stalker type stuff you hear about in the news where some infatuated admirer murders someone he has only ever seen from a distance.

That kind of crazy isnt what made Deadpool famous, its not what he's known for, its not what the fans pay to see, so for all of those reasons I'm going to say it is out of character for him to behave in this manner.