My thought is that you shouldn't have to feel torn between these two men. Like you said, they each bring something unique and valuable to the table, so why not stay with both of them? Of course, you still have to divide your time between them, but you shouldn't have to divide your heart. Love is an infinite resource.
"Can we stop ourselves from falling in love?"
Possibly, if we have enough to distract ourselves, and sufficiently refrain from the company of those we might fall in love with. But my question is, "Should we stop ourselves from falling in love, even if we can?" Polyamory is all about the goodness of falling in love with more than one person. It's about having faith that one relationship won't disintegrate just because a second relationship gets under way.
I can't think of any reason why you can't be close to R, and H as well. Each relationship is different, just as each person involved is different.
I wonder if fear is driving your feeling of being pulled in two directions. Fear that you won't stick with R, or even that you'll break up with H. Perhaps you're questioning your own ability to be polyamorous. I think the trick here is to take things a little at a time, not try to figure it all out at once. When you're with R, be with R heart mind body and soul. When you're with H, be with H heart mind body and soul. Rather than choosing R or H, choose both. That's my advice, anyway.
It shouldn't be a dilemma to have the love of two wonderful men, it should be a blessing. Just make sure you reassure R as much as you can that you aren't about to leave him. It seems to me that you have a very strong, positive relationship with both men. I can't see either relationship as being in danger of ending.
Just curious, have H and R spent much time together (e.g. as platonic friends)? If not, that might be a good thing for them to try. That way, they won't so much feel like they're in any kind of "competition" with each other.
Your poly relationships are unique, and you have to figure out what works best for you. Just try to think of it as a positive, rather than as something that might cause you to lose one relationship or the other. I have more faith in it than that.
With sincere regards,