<human>: Can you condense the text into a few key points?

I (F36) am trying to be a grown-up about this situation, but I think I'm about to lose my shit. 

My boyfriend (M45) has always had open and/or poly relationships. I'm the only monogamous relationship he's been in in a very long time. We've been together for over 2 years, BUT his female friends/former lovers cannot seem to understand that he's "taken". This happens a LOT: girls are all over him (he's a beautiful man). They cuddle him, kiss him, grope him. They're accustomed to him being free to play. 

There are three very specific women who cannot seem to get the message. I've talked to my boyfriend about it and he does try to put a stop to it. (Drunken girls don't always pick up on social cues and drunken boyfriends don't find it easy to tell hot girls no.) 

I'm not a jealous person and I'm almost never an angry person. But these few people are making me feel insane. 

I asked my guy if I should take the initiative and explain that we are, in fact, monogamous. He says he'll take care of it, but these ladies aren't getting the message. 

At what point do I step up and confront these ladies? I'd love advice on exactly what to say without being a complete bitch. I don't know how to firmly draw this kind of boundary.
<bot>: Boyfriend's former partners tend to assume our relationship is open.  I feel disrespected and don't know if I should be the person to tell them to back off.