Help I have a phsyco as a friend and my husband is just as bad?

I have known a friend of mine for a while and over the last year or so I felt sorry for her because she suffers with Bipolar and because of this has lost a lot of friendships due to her threatening them or abusing them she has two young children and has to cope on her own. Lately though she is really getting to me and I just want to stay away as I am under enough stress at home as it is but she is very vindictive and nasty and the only reason i keep going there now on a weekly basis is because if she gets cranky with me she will make up stories and turn up at my house and say **** about me to my husband (who mind you is just as psycho ) and he would believe her and probably harm me. Im sick of being scared of everybody and trying to keep everybody happy to prevent being hurt and the only reason i do this is because I have 3 children that are my life and I never want them to be hurt emotionally or physically. The day I get the guts to leave my husband is the day i can stand up to everyone else. does anyone have any suggestions on how I can get this girl out of my life without her loosing it. she is that much of a trouble maker she actually rings police on people with false allegations.