It is normal, when a relationship is new, to want to keep your new partner happy, but it should not be at the expense of your existing partner. I commend Keith for wanting to make his metamour happy, but I know from experience that husbands can get resentful of "compromising" their needs/ happiness for another significant other. Runic Wolf was like that towards the end with Pretty Lady, he wanted her to feel comfortable; to see that she wasn't just using her for sex, so he closed himself off to other relationships while he watched my relationship with Wendigo get stronger. Unfortunately, any attempts on his behalf to reach out to her as a friend made her feel pressured about the sex (she has issues around sex and we only had sex at most a half dozen times in 2 years) and her lack of response made him feel rejected and trapped by an agreement that was supposed to make her more comfortable.
I wish you luck!