Well, with Sadie I can understand (since she's your MC's gf in-game) I can't remember the beginning (when you are given the choice to have sex with Mia...I think it's a flashback so, doesn't count?) and I think you can avoid Mia the whole game without doing anything sexual.
Now, I don't know that 100% because like I mentioned earlier, I hit skip, picked some random choices and continued to skip.
Then I just quit because I'm too impatient and couldn't give two shits to see this to the end (so not sure if you are forced onto Mia/others) Story was mad boring that it didn't pull me in or hook/interest me till the end. Lots of written dialogue though... even skipping through it takes time...
This one was just not for me.