also, strictly speaking a one-night-stand is a relationship between two people who relate to each other for the evening or the night. i realise that's not how the word relationship is usually used, but in terms of dictionary definitions it is correct. they do relate with each other for the period of time that they spend together and therefore it is a relationship albeit a relatively short-lived one.
chemists talk of the relationship between substances, academics talk of the relationship between ideas, the word relationship has many many meanings.
i have a relationship with my bank, it isn't a loving or a sexual one but it is a relationship! my mother has a business relationship with her company partners.
i can love someone that i've known for just one night, i haven't many times and its been a while since it last happened but i have - so therefore i know it is something i am capable of. perhaps you haven't experienced this, perhaps its an alien idea to you or something you could never experience, none of that negates the fact that i have experienced it.
i have also experienced loveless sex, i am not claiming that all sexual experiences are loving, and i do not seek to negate or deny your experiences/your reality. i hope you will afford me the same respect.