All of these scenarios are YOUR CHOICE, none of them have to happen if you don't want them to, simple answer to the first scene, don't drinks loads and don't smoke weed."Sorry" but the game is, to say it nice...bad. There are so many choices where you do something small/simple and it escalates into stuff you dont even want...
i.E.
Party at the museum: You drink, smoke and you not only get fucked by the one guy but instead get gangbanged, assfucked by the driver and later on even from the son... I mean WTF?! Another problem is, at some point, you cant even deny it anymore...
At the massage parlor: You get fingered, then the action with the cousin and out of nowhere it switches to a gangbang... again.
There are absolutely no hints that you get used like a park bench after every single time you buy a coffee or what not...
Oh and the MC gets so dumb that she believes almost everything. "Trust" should be renamed in loss of iq. -> Priest says he will cleanse her, faps and cums in her mount and she belives that it was a good ritual...
The second one, don't allow the extras and she won't get fingered and fucked or pissed on.
As for your issue with 'trust', that is the point of the game, that she is too trusting and needs to 'wake up', but with that particular instance you mention, don't confess or tell the priest everything, then you'll avoid the scene.
EVERYTHING that happens in this game is YOUR CHOICE.