The reason it's so hard to pin down a definition is because it is an emotional experience and therefore it is subjective (subjective is still valid, but is not objective). Subjectivity means it is based on personal experience, such as your cultural, religious, family, or personal history. There can literally be as many definitions of romance as there are people on Earth. For me, I consider romance to be similar to a close friendship with the addition of components such as sexual and/or physical intimacy; passion; limerance; verbal, legal, or implied commitment; often an expectation of longevity; and the non-passive intent to be romantic. Obviously not all of these are required as would be the case in an asexual romance likely not including sexual intimacy.
Or we can just decide to define it as lovey-dovey weirdness that none of us understand.