Welcome to our forum.
If you aren't able to leave R, then you're pretty much at the mercy of his mindset, whether it ever changes or not. I guess you can hold onto polyamory as an ideal you wish you could practice, but have to turn it away because of R's mindset.
It seems unlikely to me that R's mindset will change. If anything it may tighten up: He may decide he's not okay with you being with women either. In any case I don't see you having an opportunity to pursue a relationship with T.
Sometimes people change, but it can take a long time if it ever happens. Maybe in 10 or 20 years R will have some kind of personal epiphany and decide to give polyamory some more consideration. Like you said, right now he is resisting your attempts to give him poly material to read.
I am sympathetic for your situation, and if it helps to have a forum for venting, this is a good place to go. You might want to start a thread on our Life stories and blogs board
If you are looking for advice on what to do about R, that's a different story, but I'll try not to venture into that territory unless I'm sure you'd want that. Right now I think that you already know what you have to do, and you just need a place to express what you hope for.
I hope Polyamory.com helps.