Call

What you're describing sounds like domestic violence and abuse - rape is often part of the dynamic.  Anytime one person forces another person to engage in sex, it is considered rape.

I would strongly urge and recommend that you contact your local domestic violence hotline and talk to the intake person.  These people can direct you to the proper agencies that will be able to help you, and I would urge you to do this as soon as humanly possible.  In between making this crucial call and taking action, I would also suggest that you sit down and develop a timeline as precise as possible.  Including approximate dates, times, direct quotes/threats (if you can remember them), and deliberate actions will help you, immensely.

Talking to friends about this relationship is not going to help you, at all.  Unless someone has experienced domestic violence or is educated about it, they make assumptions that victims always "ask for it" by remaining in the relationship.  This is why it is imperative that you contact your local hotline.  You may also want to visit the following site just so you realize that you're not nuts and that your desire to "protect" this person will likely be a huge mistake for you:  www.ndvh.org

Brightest blessings to you.