Ultimately, everything in a BDSM relationship (whether pro/client or civvie) is negotiated.  There is always consent given, discussion of hard limits, and "check-in" talks, re-evaluation discussions, safewords, etc.

In the final analysis, the sub (oddly) is the one with the real power.  Without consent, there is no longer a power exchange--it just turns into (real) slavery, and/or an abusive relationship, rape, molestation, or whatever.

Nobody can "force" a guy to suck another guy's cock.  If you want to play out a scene where a mistress "forces" you to suck another guy, that's just saying that you want to somehow rationalize a  way to explore your latent bisexual or homosexual interests ("Well, I would never do that normally, but my Mistress made me do it!"  Yeah, right....).

"Forced bi" is at its base, nothing more than another elaborate fantasy that you play out with your partner (again, pro or civvie, doesn't really matter), no different than interrogation fantasies, kidnapping/abandonment fantasies, age play, or anything else.

for some guys is not a cover for latent homosexuality but rather a vehicle for acting out degradation and humiliation for the fantasized amusement of a female mistress.