Welcome here to the Forum, a good place to be, as you will see other peoples' perspectives on your situation.
Parents are such powerful people, whether they mean to be or not. Their actions have a huge effect on their children, much more than those of another, and as a result if they are calm, reassuring and loving one has a healthy realtionship and all is well.
When the parent is toxic, and has an abusive relationship with a child then, even when grown, that child will suffer ill effects. You have a great deal of anxiety, enough for a doctor to want to offer you medication, and that makes for a very hard life, for some reason or other it seems to come along with self-blame, or it has for me.
Your mother is pushing all of your buttons, love, guilt, making excuses for her, not feeling like taking her on, and all the rest, with the fact you have a boyfriend as the latest weapon.
Do you honestly think it is going to stop or improve?
I'm very pleased you do have a boyfriend and can get at least one day of quiet and no blame, it must feel so good. If you did move in, and I'm not suggesting either way, I do not think accusing you of abandoning your family would be correct. It is natural to grow and leave the nest.
Plus if you were not there of course nothing could be thrown in your face. Like many you need boundaries, in other words when to disregard waht is being said and see it for what it is -and then say you will not continue and walk away.
Very hard to start to do, but necessary, otherwise your mother will never learn. You will probably need help to even start to do this.
Having an anxiety condition is a horrible thing and it is most often not possible to make yourself completely free of it. So you do need help. May I suggest you return to your doctor - without your mother, and get his opinion while you are alone. It may be he will suggest medication, it is up to you to accept or not, he may suggest therapy, which could do a lot of good.
The other thing an anxiety conditon needs is for the cause to be removed, at least for a while and from what you say that means a rest from your mother. Do you think that might be possible? My cause was my work, and in time without it I improved a lot.
It is a pity your father is away so much, perhaps he too finds home life difficult. Really I'd suspect your mother ought to visit the doctor too, and see if her anger and upset can be reduced.
I hope you come back and talk some more