The Witcher 2 romance

There are 5 confirmed romance options in the Witcher 2, though the term romance is used loosely since most of the encounters are meaningless sex. Triss and Ves are the only romanceable characters in the sense that there is an actual depth and consequence to the relationship.

Namely, these are Triss, Ves, The Succubus, an elf, and prostitutes at either of the two brothels. It is unknown whether engaging in any of these encounters conflicts with the others in the game, so thus far it is possible to complete everything below in a single play through.

Triss
Triss is Geralt's default love interst, and the game begins with her and Geralt being in a relationship. It is easy to build your relationship with her by talking to her at each location where the option is available. You can also choose to save her in Act III when she is captured. Regarding sexual encounters, 2 have been confirmed.

Prologue
The opening scene of Geralt's story is him getting up as Triss lies naked beside him as someone enters, so there isn't a romantic encounter as such, but is indicative of one.

Act I
This opportunity arises in Act I in the quest The Rose of Rememberance. When given the option to go alone or take Triss, choose to take her with. After a battle partway through the quest, the ground will collapse beneath you, sending you and Triss plummeting into an ancient elven bathhouse. After failed attempts at escape it becomes apparent that you will be spending some time here. Talking to Triss and suggesting that she take a bath will initiate a sex scene.

Ves
Ves is the first woman to appear in the story, and is the only other character aside from Triss who is actually romanceable.