Hmmm....not exactly sure this counts because we were married.
But he hired a PI to follow me. Besides following me around, the PI stole my mail, went through my garbage, and who knows what.
Re the mail: The PI would put it back in the mailbox the next day. I wouldn't have had a clue because he did it while I was at work, but the neighbors saw him and told me about it.
I did find out one nice little fact when all that was happening. The PI would park his car in my street to watch me. If I saw him sitting around, I'd call the police non-emergency line. Tell them that there was a person sitting in a car that didn't belong in the neighborhood. A cop would roll up on him and ask him for ID. The cops never did anything else, but it was pretty funny to watch through the window as they rousted the guy.
My ex used every tactic he could find to delay the divorce. It took me 3 years to finally get it done.
He did it for a couple of reasons--or at least the reasons he'd actually admit.
He wanted me to give up and beg him to take me back. He wanted me to admit that I couldn't make it on my own. That I needed him because I wasn't smart enough to survive without him.
He wanted to be sure that I didn't take any of "his" money. According to him, all the money was his.
He didn't want me to get involved with any other guy. Because when I finally gave up and came back to him, I couldn't be a slut. So, interfering with my social life was "for my own good."