(((Nucking Futz))) - I'm sorry this is happening but as the others said, you're taking the right steps for yourself. Is he on the right meds - this might be why he's sexually promiscuous, in addition to being manipulated by that woman. It sounds like he has problems with being assertive and dependent on women - his mother and this woman.

One red flag is - he doesn't have a job. As you said, he has a pattern with this woman and you would end up hurt by this. I think he and the woman suffer from co-dependency issues. It's fine to be friends with him, just guard your heart. You're right, you deserve better.