Okay first: I don't have any advice for you. I have no idea what to do in my own life, let alone in yours!
But I can tell you two things:
It seems a bit unfair to me if she's rubbing all this exciting sexual stuff she's doing with another guy in your face when she doesn't seem to want to do it with you. I don't want to be like "Mrs. Chandelier, YR DOIN IT RONG," but... I can see how that would be hurtful. I may have reacted with similar grief. Don't feel like you're crazy.
I hope that date nights will set things back on track. I want to make sure she is being considerate of your feelings here.
I can offer you some words of hope, though. I will have to say that starting things with a new partner sort of ramped up my libido in general, and I ended up stepping up sex with my husband also as a result of having this new romantic adventure. Maybe--just maybe--this might happen to you. You never know.
What does she say about her "funk"? Does she say it's fading because of all this new sexual excitement? Or is she just in a funk around you, but not the new fellow?