When to fight, and when to back down Options

[MissFits]

There is this girl that used to date my fiance.
She still writes him up on myspace every few months and tells him she still loves him and takes any opportunity to talk shit about me.

Recently her boyfriend got sent to jail and she sent a message to John saying that now that Nick, her boyfriend, was in jail and they should be friends now. She kept saying things to him that made me uncomfortable and I wrote her a message that wasn't rude at all but asked her politely to get the f**k out of our lives. She suddenly got very defensive and started verbally attacking myself and my friends. I then sent her a mean spirited message back that told her if she had anything to say to come say it to me because I was at a pretty well known place in my area.
She never addressed my offer to talk face to face but continued, rather, to talk shit via myspace about various loved ones I have and then she crossed the line when she made a comment about my dad killing himself.
My dad died of a drug overdose 2 years ago and it was a complete accident. It straight up INFURIATES me that she would go that far, but it is not the first time she has done it. I forgave her the last time because she had moved to New York and there was nothing I could do about it.

Now she is back in my home town. She still writes my fiance on myspace and has her one and only friend talk shit to me and about me any chance she gets. Normally I would just crush someone for doing these things but the problem is she is 17 and I am 18. That is assault on a minor and it's a felony. I am not trying to go to jail for 6-12 months for this bitch, what do I do?

[MissFits]

Oh, but wait! Things can't ever be this simple for me. Oh no, not at all.

My fiance and I have been having minor problems for a while now, and it has gotten to the point where we are a completely different couple than we used to be. A lot of minor problems make big problems, they are like legos I guess. Well, him being too nice to his ex girlfriends that still want him has always been a problem. He can't stand to be mean to people.

I found more messages to and from her today, even after she talked all that shit about my dad and family. He left me at a friends house to take a drug test at 11 and didn't come back to get me until 5. When I asked what took him so long he said he was physically and mentally preparing for the drug test (he had to fake it to pass it) and I found out he had been talking to her.

I just don't know what to do. He didn't say anything out of line to her but the fact that he will still talk to her kindly even after what she did to me really hurts me, and it hurts me even more that he lied to me about it.

I have never had problems like this, I am absolutely stunned.