I don't think you really know until after the relationship ends. I've got two ltr exes that I still hear from many years later. They have both told me that no one will compare. They've both asked if I would ever get back with them more than once. They have both seen therpists to try and process things and move on. They never were as attracted to the guys that replaced me as they were me. They have both entertained the idea of leaving their current ltr to be with me.
Now, during the dating phase a girl that is super into you will be very supportive, cause little to no drama, cook for you, lots of sex, no complaining, no bitching, willing, follow your lead and she won't mind if things aren't balanced. She will treat you like a King. IF the connection continues to develop overtime you have a good chance of being her #1.
And to answer your question about the girl you never had sex with, no its not likely. Thats just infatuation/fantasy/lust/dreaming/an ideal/seeing what they want to see and not seeing the entire picture.
I feel sorry for the guys that don't understand why you need to be #1 in her life and those feelings she has need to run deep if you are going to make it long term. It also helps with respect, support, bitchiness, compliance, etc.
The better you are socially, the more you will influence, understand and connect deeply with women, and the more that will lead to long term success.