Wow, sounds a little crazy in his family! But I think if you don't give them anything to bit$$ about you, then they have nothing to say.
I'm glad your H told you that. Mine is not able to express himself that way, so I have to look for little clues all the time--tiring!
What if you had to stand up for your health and that of your baby? I know it's hard, but I think your GF's boyfriend and, maybe her too, are taking advantage of your inability to draw a line. I really think you have to stop it now.
I don't want to hurt anyone's feelings either and I think that is what you are afraid of. If your friend loves you she will eventually understand. If she doesn't then she's probably not good for you. What if you get to the point where you do explode? I think a nice adult conversation between the three of you will get better results. Come at it from the angle that you are having stress-related health problems. You shouldn't be bleeding because you are under stress. You know your baby can feel your stress too. Emily, this would be a huge step for you toward confidence in yourself and treating yourself better. It really is ok to be a little selfish. You don't have any problem letting your H know your feelings about his family, you can surely let your friend know things have to change.
I think it might show your H that things are changing in you if you can do this. Something's got to change Emily and you are the only one who can do it. You don't want to go back to the same old M cuz somebody is going to be disappointed, unhappy and resentful. This is one thing you can do to add to your confidence. And it sounds as if it really is for your own health and the health of your baby.
If you have a counselor or therapist, it would be helpful to go over this issue and get some help learning how to draw a line to protect yourself.