I just watched this on Netflix a couple years ago, and it was pretty new. Maybe 2010 or newer, but I will say as late as 2005 to be safe.
It is a low budget indie type film, well made and doesn't look or feel cheap at all. A young newly wed couple honeymoons at a cabin in the lake. Basically the wife ends up disappearing at nights into the woods where the husband thinks she's cheating on him or was raped by a neighbor or something, but it turns out she was being mind controlled by an alien who may or may not have impregnated her(i don't remember.) In the end, she takes her husband to the middle of the lake in a canoe and throws him in the water with something heavy so he drowns.
The actor and actress were attractive, it was a great plot twist at the end and it was an interesting movie that I want to rewatch. It was available on netflix streaming when I saw it but I don't know if its there anymore, I can't find it.
I think it was called HONEYMOON. I rented it at Hastings earlier this year.
Indy is spot on. That's Honeymoon. I actually quite enjoyed it myself!
Starring Harry Treadaway (I think he's Frankenstien in Penny Dreadful though it may be his twin' and rose 'you know nothing Jon Snow' Leslie