While I'm with you that I don't like NTR, it can't technically be considered that since it's sharing, not cheating and it's completely avoidable, if you saw some scenes then it's due to your decisions, and yes, some can be quite misdirected but it'll be pretty obvious most of the time, and well, the slut and pure routes only changes her behaviour and dialogues in certain events, in whether she's more open sexually and more comfortable being nude publicly and yes, whether she's able to be with someone else if you decide it like that.
For Adrian, sadly the "only" girl that he likes is Alice so you have 3 options, steal, share or leave her to him, and I know, it's a complicated choice since seeing her with someone else might be a bit weird if you're not into sharing and stealing her might make you feel bad for Adrian, I choose to steal her since I can always share Sam with him as well. For the dialogues saying that he's not as big as you, the difference is not that big and it seems to be the average in that city/universe, the MC only got a bigger one, the girls also have unrealistic breasts, waist, ass size that not every woman you meet has so take it as it is, only fantasy.
The Joseph and Anna point, while yes, it feels sad that Joseph felt like he let the entire family down and that his wife is cheating on him, he also can cheat on her if you tell her about his ex wife and you so it's not like he's that innocent either, he's a good man trying to provide for his family but good intentions aren't always enough, if this was another game then it could've been different, but the premise is that you help your "milf", his wife, to do a porn page to help with the debt, so if you read what the game was about then you knew what was comming. It's kinda the same situation as Alice's, steal Anna or share her, or you can just ignore him and pretend he's not there since he' almost always in his office and you might not see him, just in special events and Fridays.
Buddy, I'm sorry you're going through some rough times and that this game hit you different with some things, I've been there with other games, just remember, this is only fiction and fantasy, size doesn't mean everything in real life, someone skilled with hands, tongue and knows what he's doing is way better than someone with just a big dick, and if someone tells you otherwise they're just lying, exaggerating or have the mindset of a 13yo. I'm sorry about your gf, as some have said before, you found this game at a wrong time, take a break from these games and content, focus on yourself, try to be a better version of yourself (for you, not others) so that you can be at peace with who you are since you might be creating an unrealistic expectation for you, go to therapy, gym, find some new hobbies, focus on what you can change and try to accept what you can't, I'm not saying do a 180° change and stop doing what you like, just try new things, a fresh perspective is always good when you've been in the same spot for so long.
I wish you the best, don't listen to the people that is saying "it's just a game", even the tiniest thing can trigger something big at the wrong time, place and mind.