Occasion of sin includes doing something innocent that leads to other things, or could easily lead there, even if it does not.
When I was young and dumb and poor, there were times when I traveled with groups of friends of both sexes. If people of different sexes slept in different beds, on different couches, etc., nothing was going to happen. If people of different sexes slept in the same bed, or were encouraged to do so, it was pretty obvious that something was supposed to happen. If people did not want something to happen, the guy or girl slept in a chair, or in the bathtub or shower or closet, or sat up reading all night in the hallway or the hotel lobby. I was always having to draw clear lines about my own behavior to prevent dangerous misunderstandings. I was not sinning, but it was an occasion of sin - and if I had been drunk or into drugs, or too sleepy to think straight, I could have put myself or one of my friends into a very bad position.
After a while, I got money and sense, and was able to have my own room when I traveled, or share only with friends of the same sex. There comes a time when it is not fair to try to treat people as both honorary siblings and as unrelated persons of potential romantic interest. You cannot have things both ways, and it is not fair or safe.
Even if you are just at a party or hanging out at someone’s house, you need to put some thought into how you behave. If you are in love with someone, you need to treat that person and yourself with respect. Don’t create a bad situation. Think.