Hi Abhainn, just a word of encouragement from someone who has felt herself to be the inexperienced/slightly boring partner and actually asked the more experienced one to teach her;
Don't assume just because somebody is more experienced and willing to act as your teacher that YOU have nothing to teach them. Each partner, I find, is able to teach us something new, and we to them. Things you used to enjoy with partner A might not be on the table with partner B, and that doesn't necessarily make partner B less interesting. Feeling lack of interest in sex with you might also be a consequence of him not feeling he can be vulnerable, willing to learn, modify his style etc.
Like a friend of mine (considerably more experienced than I am) put it; there's only so much you can learn of the basic technique. Once you have the technique, good sex is 50 % enthusiasm about your partner and 50 % compatibility.
Me: bi female in my twenties