When I first read the title, I automatically assumed that this was another hoax from someone seeking attention. But I read further, and this at least seems somewhat genuine.
It's sad that people like your mother exist, and I'm very sorry you had to experience what you did. Society at large is still somewhat uncomfortable with addressing issues of incest, especially ones as depraved as this. But the fact that you were able to ask for understanding in such a mature way indicates that there's still hope for mankind to eventually learn how to confront these issues on a large scale, and help eliminate events of incest before they happen. Like any other societal issue, the first step to solving the problem is to increase awareness.
I was molested by my own brother when I was much younger, and I can understand the feelings that go along with that. You may feel that her forcing you to do those things was partially your fault, because you "gave in" to them. That's not the case. This is 100% your mother's fault. She knew that what she was doing was wrong, and when she knew that you were resisting, she resorted to blackmail.
I'm not sure how old you are, so I don't know if you have access to school counselors and whatnot. If you went to one of them, they would be required by law to report to the authorities. If that's what you want to happen, then please take that route. Some people seek retribution for their molesters, and want them to meet justice however possible, and believe me, these people deserve it. Others, however, choose to instead remove themselves with the situation completely, and don't concern themselves with revenge or justice because that would mean still having to deal with them. If this is the course you'd rather take: that's ok too. Molesters like your mother will meet their fate in one way or another. Until then, if simply cutting off contact with her will allow you to grow and mature in a healthy, positive way, then by all means, do. If the contact you'd have with her during the legal process would only hamper your personal growth by re-hashing so many negative emotions, then trust me-it's not worth the effort. Just do what YOU need to do to move on.
Believe me, that type of mother/son relationship is NOT normal. If I were you, I'd spend my time trying to pursue and maintain other healthy relationships--whether they be of the platonic, friendly, romantic, or mentor/mentee variety. That way, if and when you ever become a parent, you will have enough experience with healthy relationships to break the cycle of abuse that so often occurs in cases like this. The psychological damage that your mother inflicted on you is major. But if you focus on the positive, and give yourself all the credit that you deserve, you can undoubtedly overcome it.