Romance usualy focuses on developing a monogamous relationship with lots of conflict and a happy ending.
As far as erotica and romance, well
erotica~ lots of explict sex (doesn't always have to be monogamous, doesn't have to do with emotion)
romance~ the sex isn't so explicit or as often as in erotica, but has to have emotion and commitment.
Then there's erotic romance, which is all the explicit sex with emotions and monogamy, and sensual romance, which also has the steamy scenes and lots of them, but still focuses a lot on the relastionship and conflict. The lines are blurred a bit, so take your best guess.