All of our romances are relationship based. While they may contain explicit language, the story and relationships between the characters involved will always be the key. Erotica, unlike porn, is about the relationships and the story, not just the sex.
These books are more about the romance than the sex. While the story may contain some erotic scenes, sex will be behind closed doors. Exclusive relationships between two characters committed to each other.
These tales will give you a bit of a nip. Relationship is important, and the basis of the story, but these will feature sex scenes and stronger, more explicit language. These will still be strictly relationships between two committed individuals.
These stories will start to push the boundaries. There may be light bondage in these and perhaps more than two individuals within the sex scenes. The sex scenes will be detailed with very explicit language. However, the storyline is still queen.
Careful. These books might just cause you to burn up in flames. Light bondage, anal play, multiple partners, swapping partners, bisexuality and in depth detail of frequent sex scenes with very explicit language can be found in these novels.
There is a reason this is termed "beyond "sizzling". The bondage might be a bit intense, as are the sex scenes. You may also find fisting. This is extreme, but still within bounds of consensual sex, etc.