The line is there, but it isn't as defined I think. For the most time I know which people I am interacting with because I want to have a relationship with them and which ones I am because I want to be their friend.
1. Yes, quite often. Also with your SO. 2. Then you don't sleep with them... It isn't like sex is the one and only start of a relationship (even if it is a common one). We have done this from a really young age and you don't have sex when you are 10, so the social rules and signals are ingrained in us so sex does not need to happen for you to be in a relationship. I know of plenty relationships that didn't start with sex, including mine.
Re: I had a thought:
1. Yes, quite often. Also with your SO.
2. Then you don't sleep with them... It isn't like sex is the one and only start of a relationship (even if it is a common one). We have done this from a really young age and you don't have sex when you are 10, so the social rules and signals are ingrained in us so sex does not need to happen for you to be in a relationship. I know of plenty relationships that didn't start with sex, including mine.