Well, it's true I installed the mod that shows you how many points + or - you will get for each decision, but I did not know exactly what would happen in the story, and both when I got William, and when I didn't, I followed almost the same logic till there, just changing that one decision. I just followed my understanding of the character.to the opacity of the choice. Once I became aware that it existed, I bailed on Bobo ASAP (because, again, I don't enjoy this sort of content in corruption games), but if I'd known I could be relatively kind and still get William, I would have. So Myriam acted like an asshole when she didn't have to, but in my defense: how was I supposed to know she didn't have to without looking at the code? Without doing so, it's an either/or choice.
I don't want to take too seriously the game, but Myriam has from the start a maternal, protective and sweet side, and even if one continues in that direction and even pushing on the "refrain from confrontation" directly to the "submissiveness", that does not mean she cannot overcome her fear to protect "her own" (in that case, Bobo, who was nice to her).
That would be actually very coherent with her being "big momma" (I am not referring at the cm of her boobs and ass , though she is also well developed there ;-)) - know the joke (which is actually not a joke) about mother bear, or about the mother of the wild boars ?
Effectively, if you play in a certain way you can see how even the way she calls Marc ("duckling"), the way she worries about "traumatising" the little $#%, how she is afraid for what Anthony can do if discovers him in a certain situation (personally, I did both the "kick out" and "keep in" scenarios), how Marc tries to get its way by exploiting that protective motherhood sense with stuff like "it hurts so bad can you help me" and making her feel responsible if not even guilty for it, how she worries about losing the mother/son relation. It's true that mostly comes after the Bobo scene, but it does still go in that mothernal direction.
So, for me it was natural she would anyway help Bobo, at least to a certain extent.
By the way, I do hope there may be situations where Bobo and/or (preferably "and", but separate ) the underpass bullies will come back in the game, but if Zorlun keeps going the way he did till now, I am sure he will let you (well, Myriam) decide whether to "get there" or just interact in a different, non sexual (even if positive) way with Bobo.
So, don't worry, I don't think that helping Bobo means you (well, Myariam) will automatically have sex with him.