I. Need. Help. Please.

I think anda should sit your mother down and explain how you're feeling. Explain to her, that anda are 15 now and quite capable of travelling on your own, anda are responsible enough to know about the dangers of the world, and she can trust anda to call her if anda need her. Also explain, that just because she no longer loves your father, she has no right to say horrible things about him to you. Whether they are true atau not. he is your father, end of, and if she can't accept that and let sejak gones be sejak gones and be civilised about it, then i'm sorry but she is very immature.
Explain that because your mother keeps saying these things, anda feel intimidated about wanting to defend him in case she's angry and that neither parent should try to force anda to choose.
Just tell her that anda understand why she could feel this way towards your father, but it would be nice is she restrained those feelings away from you. anda don't want to hear these horrible things about your father, as he's your dad. If she comes up with the excuse 'but anda don't know what he's like' then just explain that anda feel your old enough to find out for yourself without any preconcieved ideas out of spite.
Just tell her that with the way she's Berlakon anda feel very disappointed and horrible and that she's trying to stop anda from seeing your father.

If talking to her doesn't help, try talking to your mothers new partner, see if he can make her see sense. If not, what about your dad atau your dad's new partner?
anda could also try looking in your local phone and address book to see about family legal aid and find out your rights about your parents divorce and whether anda have a leg to stand on if anda wish to go to court against your parents to actually sort this out.
How about councelling, not for you, but for your mother? It may help her. Family councelling could also help anda get your feelings and ideas across to your mother without her rejecting them without a proper explanation.

It sounds like your mother has alot of hurt feelings that she has not let go of. It is sad that she puts it all on you. I agree that anda might want to try to get another adult to mediate between anda and your mother. Maybe that way she would see how unfair it is to talk badly about your dad around you. I don't mean to pry, but anda did not say what country anda and your mom live. In parts of the US, a child may decide who they wish to live with at age 16. It would be unfair to put anda in that position. For now, try to keep in contact with your Dad best anda can. Try to remember that your mom is angry with your dad. anda should base how anda feel about him sejak your interactions with him. It's hard I know, but try to treat your parents with respect and maybe your mother will listen to you. If anda have a school consoulor atau minister anda trust, speak to them. I hope things work out. Let me know if I can help.