I cannot relate to being a step parent but I know that it must be difficult, especially when your H lets his kids disrespect you. The son's comments sound manipulative and hurtful. There are definitely some jealousy issues that have not been handled well.
Have you looked into Al Anon? Some of your behavior is probably learned from seeing your mom cope with your dad. I've been going on and off for a few months and it has helped me tremendously. My grandparents drank and I learned some bad coping skills from my mom because of it.
You definitely sound like I did a few months ago. I didn't really eat for weeks and when my H talked about wanting me out, I would pretty much feel physically ill. I've slacked off at work and it became hard for me to do much of anything.
For now, try to do things with your kids, friends, family, etc. to get out and GAL (get a life) to prepare yourself for what may happen if you do go your separate ways. Once I accepted that I cannot change my H, his thoughts, etc., things began to get easier. And once I accepted that he wanted to D, even though I didn't, I started to move on with my life.
You may need to call your GP's office and tell them what is going on and that you need to be seen. I did not right away. I finally called my OB/GYN because I felt out of control with my emotions. He checked my hormones, which were really low. From there, we increased a dose of 1 AD. When I finally went to my GP, I had lost so much weight that he wanted to treat me for an eating disorder. So he changed my meds and it made all of the difference in the world.
Sometimes it takes time for the meds to get into your system and work, so the longer you wait, the more miserable you are going to feel.
It does get better. It will take time to get over the shock and the hurt.
M44 H57 D17 (special needs) M 18 yrs Bomb 7/2/12 Still living together