Ugh, Sue, I'm so sorry. You're right, you can't do anything about Melissa's choices. Unfortunately, it sounds like neither one of them treats the other very well. What you CAN do is hold Melissa responsible for how she treats you and husband. When my difficult child was in an abusive relationship, we basically sent her the message that if she wasn't going to get help or get away from him, we didn't want to hear about it. She was not allowed to take it out on us. Tell her she can go sulk in her room. If she tears it up, or continues to be verbally abusive towards you, tell her she'll have to find another place to stay for her next school break. Seriously, you don't need it, want it, or have to put up with it!
I know, I know, your husband is a sucker. *sigh*. Good luck with the job hunt. If you need to get away in the meantime, how about the library? Find a good book or magazine and a comfy chair, and enjoy the quiet for a couple hours. Barnes and Noble is good for the same thing, and you can treat yourself to a nice cup of coffee at the same time.
I hope you can manage to detach and do something for yourself.
((HUGS))
Genny