To be clear, this is not about ltr, just difference between what it is you FEEL differently between dating a girl and fwb-ing her.

I realise that the way you ACT is prescribed by rp principles- I'm not asking about that.

What is it that makes you think 'I actually want to date and see how it goes' or simply 'she's pleasant enough to hang out with and fuck'?

Is it a romantic/ emotional draw towards her.

This is not about being all sentimental. I realise proceed with caution always applies.