The difference between romance, erotica and romantica is marked. Romance only ever hints at the sexual acts and uses rosy purple prose instead of throbbing purple pricks. Romance doesn't portray explicit sexual acts or use vulgar words, erotica does. Romance uses euphemisms to suggest sex. Erotica tells it like it is using blunt sexual words (cunt, cock, fuck, etc) rather than poetic suggestions (referred to as purple prose in the romance genre). Romantica is a combination of romance and erotica.

For assistance on learning the genre and rules of erotica and romantica see:

Erotica:  Writing and selling erotic fiction
Romantica: Is erotica right for you?
Erotica: An end to Euphemisms