If you doubt the ability for humans to sexualise robots, you need only look at news that Japanese company SoftBank has felt the need to remind users of its friendly Pepper robot not to have sex with it.

The humanoid Pepper uses a series of sensors to read the emotions of its users and respond accordingly. According to its manufacturers, Aldebaran Robotics, it is intended to “make people happy”.
This apparently doesn't extend to sexual intercourse. The user agreement for the emotion-sensing robot states: “The policy owner must not perform any sexual act or other indecent behaviour.”
Pepper has proven to be immensely popular in Japan. 4,000 copies of the 198,000 yen ($2,344) companion robot sold out in under a minute when first released, and a new batch is due to go on sale this month.
I'm not sure how someone would have sex with Pepper, but it goes to show that, as soon as you begin to humanise an object, you open it up to sexualisation.
Next: robot sex will become common