Sorry, this might be a bit of an epic 
I have an older brother, who has long had a history of bad r/ships with women. His usual pattern (and by 'usual' I mean 'that this is exactly how all his r/ships have progressed since he was 20, - he is now in his 30s) is to have a LTP, on whom he cheats with a succession of one night stands/short r/ships. After a few years with the LTP, - who, by now is talking about moving in/getting engaged etc - he finds another girlfriend. The old and new girlfriends overlap for a few weeks, often with him breaking up and returning to the old one a few times, until he then fully moves onto the new girlfriend, who usually has no idea about the old one. She then becomes maitresse en titre, and he proceeds with the ONS and, eventually her replacement.
Over the years, I have become more and more concerned about his attitude towards women, - I am really beginning to think he doesn't like them, even hates them. He talks about going to strippers and prostitutes, how he prefers boob job breasts to natural ones, (not because of a size/qualitative issue, but just because he likes the idea of a woman altering her body to please a man, - he has explicitly stated this) he has told me about putting pressure on partners for anal sex, and so on. He also seems to enjoy hurting women and having them still want to go out with him. He has never had a functional r/ship with a woman, and he has no female friends. In fact, he has very few friends he has known for longer than 2 years.
He is my brother, and we have always been close. But this is making it harder and harder for me to like him. He also seems to want me to know for some reason, - he has always come to me and told me these stories, as if daring me to flinch. He also phones me up regularly when it all goes wrong, crying, flagellating himself for how he's behaved, and promising to change, He never does change, natch. He also lies to me, (as well as everyone else) - you never get the full story about what's going on, only just enough to make you feel sorry for him. He has had a few MH issues/brushes with suicide in the past, and will sometimes hint at this if things are going especially badly.
This christmas, he is currently in the 'flitting between two LTR' stage, which he has assured us is 'all sorted out' but then made it pretty clear to me that he is still involved with both of them. This put me in a difficult sitch with our parents, who are worried about him 'not being happy' and him being involved with 'predatory females who won't take no for an answer'. I had to do some pretty hard tongue-biting over that. One day he disappeared off to see current maitresse en titre, but I strongly suspected he was in fact with ex-girlf. I knew he would want to talk to me about it, but I had had enough. When he pushed the point, I told him I didn't want to hear and asked him to leave.
So, what do I do? My current plan is to refuse to talk to him about anything connected to sex/love/his private life ever again, but that is difficult. He drove me to the station and kept trying to get me involved, - even to the point of calling one of the women in front of me and making plans to see her. He keeps hinting and sighing about 'being on his own for NY' but I won't bite.
But do I have a duty to do more than this? I am beginning to be worried about what sort of a man he is, and the damage he does to women. Should I tell his current girlfs what is going on? Should I tell our parents? Should I confront him in strong terms, call him a misogynist and advise him to seek professional help? (he has had concelling in the past but has not stuck at it).
Thanks to anyone who got this far