Stress and Pregnancy at 26 weeks

How bad is it to be severely stressed during pregnancy? The whole pregnancy this far has been stressful. I have major depression and a personality disorder and am off my meds. My boyfriend is a recovering addict but has had several minor relapses in the last few months and then a major one last week. My dad is very sick and requires me to be his full time caregiver at the moment and to top it off I have 3 kids and no one reliable to help with them. I got to the point today where I called a crisis line to talk me down from self harm but the amount of stress I feel right now is unbearable. Does anyone know how this can be affecting my baby, I've been so anxious and crying uncontrollably and randomly off and on. Are my risks of preterm labor higher due to stress? What else can stress hormones do to my baby? I don't even know what I can do to eliminate what's happening. Abandon my dad, leave my fiancé? That leaves a whole new level of problems. I can't just snap out of this ladies. It's a real mess. I want a happy healthy baby and I want to be healthy and happy and able to care for her. I'm just so sad right now. Any advice or words of encouragement from someone who's been through or going through this would be nice.