Well! I can understand how you feel! This is not the weirdest story that I have heard, but it is close.
We have a Mayor here who did the same thing as your mother.
She also married her daughter's ex and now she is her daughter's child's stepmother. However our Mayor is also a nut -she tried to commit suicide, drove her car around a golf course at night and had a picnic with her man in the cemetery at NIGHT. They used her limo amd it rolled back and crunched a few headstones.I could say more,but it is just a dumb stupid tale.
You are entitled to feel precisely as you wish to feel about your situation. Do you feel somewhat betrayed by your mother? Everyone else around you will have their own take on this and you do not have to agree with any of them if you do not wish to.Also you do not have to listen to them dictate to you as to how you should feel. Point out firmly that you have your own perspective on this and you will not have them critise you or tell you that you are wrong. Tell 'em to buzz off....Jac