I realize that you are horny and feel unappreciated, but it really does look like you're putting way too much emphasis on the sex act. When I said that your husband might be burnt-out from trying to keep up with you, I didn't mean it like how many times per week do you expect him to fuck you, I meant it more along the lines of being made to entertain responsibility for your feelings.
You have specified numerous times that you know he appreciates / desires you but that you just don't FEEL appreciated / desired. What mmore can one person expect from another. He can't get inside of your head and make you "feel appreciated / desired". Even if he has sex with you MORE than the GF, you've already set it up so that it would be "pity sex". There is a term for this, I can't remember what it is, but it's the one described by "be spontaneous". It's like when a wife wishes her husband would "be more romantic" but if she told him what she wanted and he suddenly started bringing roses and lighting candles, she'd be all "You're not doing that because you WANT to, you're just doing that because I TOLD you to. BE SPONTANEOUS!"
Srsly - I don't see this as something that your husband and/or your girlfriend can fix for you. I think you have set yourself up as the loser no matter what course of action the other people involved choose to take. It's probably a good thing that you have the triad. Normally, I'd say that it's not a good idea to add more people if you haven't worked out the already existing issues in your marriage or "primary" relationship - but in your case it appears that you have become complacent regarding certain things and the new interpersonal dynamic has brought out some opportunities to work on these issues and hopefully grow from the experience and become a better person.
But we don't know each other and you don't have to listen to or believe anything I say. I have not walked in your shoes nor have I ever been in the triad type of relationship configuration. I am also not a licensed or trained therapist or counselor.
Please disregard anything that turns out to be an incorrect assumption, because I sometimes have difficulty remembering which specifics apply to which individual on the forums. As most of you are prob'ly aware, people start threads and then go and give advice or respond to other people's threads, and sometimes the stories are sort of similar.