Send a symbol and I’ll answer the question about my muse. (Or answer in character. Whatever works for you!)
đź’‹ – How does your muse feel about people who cheat? Do they see a reason for it, or is it completely immoral?
This one’s simple: don’t cheat on Koschei. Do it once and you’re through. For good. Â
It’s not even a moral matter so much as he is tremendously, pathologically possessive. Even in his healthier relationships, he is extremely sensitive to being abandoned in even the remotest sense (this is 100% the Doctor’s fault, tbh LOL, Koschei was always on the clingy side but the Doctor’s abandonment has augmented the issue exponentially). Oddly, this doesn’t apply to friendships, or place him in the profile of the abusive spouse: he does not seek to isolate his partner from the outside world or from other relationships. They can socialize, go out, etc normally with others: it’s more that he’s eager to come with, and be shown off as his partner’s “favorite.”  All reasons why he’s an impenitent flirt with his partner in public, and loves pda. Â
Have friends, hobbies, activities, interests entirely outside of your relationship with him, that’s fine. In fact, he prefers some alone time to obsess over his own intellectual projects. But a rival romance, however, he won’t tolerate. Â
People reading this will invariably point to his brief relationship with his human wife Lucy. And to that, I say, perhaps indelicately, Koschei was never in love with Lucy. Lucy was (very badly) used as a prop. Lucy was a revenge relationship on the Doctor. Lucy was the Master showing the Doctor, quite cruelly, that he can imitate everything about the Doctor’s usual operation (youthful and energetic, charismatic, a human companion to travel with him) and yet be unrepentantly evil and past “savin,” a perverse act of defiance of everything the Doctor, who “makes people better,” stands for, down to the point of suicide in order to resist the Doctor’s promise to “care for” him ( “how about that? I win”). The Master therefore shows no interest in fidelity to Lucy. He does not consider her a true partner, romantic or otherwise. Quite awfully, he thinks of her as part of a disguise, a tool, necessary collateral, just like his pseudonym, his election, and a tenth of earth’s population. Â