Sorry for the long answer. Before the sexshop scene Darius will talk about shower after sex and ask you whether he is the person you'd like to shower with. You need to answer "no". It's not really a bad choice 'cause Darius will joke about how you did it and liked it. And then you need to do the sexshop sequence. I don't really remember what to choose but you should just try everything and there will be third choice in the last sexshop decision
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You are a godsend, I did it once by accident, maybe trying to deny I still liked him but this helped me a lot.
For anyone who scrolled down this far to figure out where you went wrong this is it
After you say no to the shower with him before the sex shop like Blideth says. The sequence is yes you like the leather, he should go for the dildo, you'll consider a dildo too, and maybe watch porn with him is the success I saw.
Thank you again Blideth