I'm not sure why you have called on me Ygirl? oh the pressure
Anyway, I am left feeling very concerned about all you say Alexandra. You say that you and your husband have had loving relationships before yet have never had sex with anyone that has come into your life in the secondary kind of way. You have said that the women your husband choices have treated you badly and you haven't really objected unless it's in your home.
If this thing with your T becomes sexual then it would follow to reason that your L would want to start having sex with the women he sees....
Major RED FLAGS with that one!
Sex will exacerbate them treating you badly and him not doing anything about it. I think you have some major things to deal with here. I am really quite concerned that if you don't deal with them you will end up being very damaged by all this.
I don't usually advocate therapy as I tend to think that people can work things out for themselves with a bit of guidance and good supporting friends, but this is huge to me as it is teetering on the edge of abuse. I suggest marriage counseling.
I would love to say that you need to stand up for yourself etc blah blah blah I am sure Ygirl and others will say just that, but this is a pattern it sounds like and could very well run deep. It sounds like both of you need some better ways of dealing with people in your lives and not letting them trample over you and run the show.
There is something rather sadistic in this whole thing. He could very well just be a bit in denial that these women are bitches to you or he could be getting off on it. If he is truly concerned that his girlfriends treat you badly and doesn't know what to do then I suggest that you have lots of things to communicate about and I would stop everything to reconnect in this way before moving ahead with T, but really I think that should of already happened and the problem should be resolved not repeated... it sounds like it never was....
It seems the bigger issue here is not T, but the relationship between you and your husband. All the rest is the same usual stuff that people who are trying to get a poly life going face and that all comes out in the wash one way or another when a balanced primary relationship is running smoothly.