I often compare preying on marriages to bullying... I think there's a lot of overlap

Both can be done in person or over the internet
Both cause the same psychological damage
Both leave no visible mark on the LBS, but they are an emotional wreck
Both are combated the same counterintuitive way - exposure
Both LBS and the Victim's of bullying are intuitively nervous of exposing the bully
Immature audiences cheer bullies on, celebrate their aggressiveness
There's often an attempt by the bully to again plead innocence as there is often no immediate physical evidence

I could go on, but you get the idea

If someone broke into my home, spraypainted my walls, and walked out with my stereo it would be illegal... but trashing someones home, their family, and destroying a marriage is NOT?

I am very much in favour of a law against third parties violating marriages...

The harassment law may fit, depending on how its worded.. and of course, how applied...