What is the difference between close friendships and romantic relationships?

su

What do you believe the diffrences are? Does one have a certain spark? Is the only difference sex? Does it just come down go labels?

(When answering this it would be cool if you could include asexual, aromantic, and none monogomous relationships aswell)

In my personal life am having some trouble finding true distinction between them so I thought if ask for other opinions!