In a new, developing set of relationships, one is always going to be running more hot than another. No two human relationships are the same at any given time, so this is just a given. It sucks that you're having a hard time with the way things are right now, and I feel for you. But would it really be better if you and your gf were running hotter and your husband was feeling like the less-desired one, left wondering if maybe he was just included because it seemed like the right thing to do? Or if you and your husband were in the midst of a re-conflagration of passion, and your gf was left feeling like the uncertain, possibly unwanted new third wheel?
None of these options are good, obviously. Ideally, all of the relationships involved would be equally hot and revved up. I just see that as very unlikely at any given time. I do think you should let her know that you're feeling a little raw about how things have been lately -- maybe she and your husband can be more considerate and tone things down when you're there -- but I don't see that she can generate passion for you if she's feeling it more somewhere else right now... passion is a spontaneous sort of thing. What she could do, potentially, is devote more one on one time to you? But you can't expect her to act more passionate than she feels, or to feel differently than she feels, even if it's difficult for you.
It seems like a very good thing that the threesome sex is still passionate and that you and she still have a strong emotional connection. It just goes to show that nothing is fundamentally broken here, she and he are just going through NRE. Or, heck, maybe in the end she'll always have a more visceral physical connection with him than with you. You'll STILL be in a position that most people would deeply envy, with two people who love you and also love each other! Buck up and count your blessings.
Easy for me to say? Well, I speak from personal experience, being in a very similar situation in certain ways. It DOES hurt. But it WILL be ok.