Does that mean the rest/minority of MPA are bi and have GFs?
IMHO, no matter how upfront the MPA about her single status, it will be delusional to believe her "honesty" unless she provides the proof or you get valid confirmation from the independent source.
The probability of creating identical deep and genuine bonds with "civilian" is no better when compared to MPA/SP.
Plus you get substantial, albeit different "downside" when it comes to bonds with civilian counterpart, i.e. she either uses intimacy as leverage to dominate you or she is too frigid in intimacy that you have to take it or leave it.
You are still a "client" when you are with a civilian GF company.
For MPA/SP, money may not buy Laughter, Obligation, Voice, Equality, aka LOVE but you definitely get intimacy.
On the other hand, for civilian GF, Equality between genders sounds too affirmative action nowadays, while fufilling Obligation as SO is not worth it when she considers you as a "jerk".
Having omitting the letters OE, your civilian GF prefers to use money you pay for her company to get LV-Louis Vutton, instead of intimacy