I know. and have seen some moments (if you don't reject Moonsong), my guess regarding Amber is that She shares everything with Mc than with Evelyn, If you don't reject Moonsong and you see how upset Evelyn is, at this point Amber could get angry with Mc or spend more time with Evelyn, but instead we see a different situation, I would say despite on the hard feelings between Mc and Evelyn, Amber doesn't want to lose them both, but prefers Mc, no matter what kind of fool he is, Amber likes to spend time with Mc, because he sees in her enough suffering than she seems!
I don't deny that Amber may have an interest in Evelyn, but I would say it is more of a sexual attraction and playful side than feelings and love... Amber may have feelings for Mc, and we saw this twice when she jerked him off, and then she kissed him, and both of them are her initiative, someone will say, “She might be in love with Evelyn,” then she could easily play with Evelyn's pussy, That’s why she’s still closer to Mc than to Evelyn, but both love in a different and different way that she doesn’t even want to lose them. Perhaps the lesbian hint and threesome is due to the fact that Amber is almost as much a fan of sisterhood as Mc, so she is interested in getting laid, it is unlikely that she directly meant that she could sleep even with Evelyn. so it's too early to draw conclusions...