The secular press has provided wide coverage to the legal aspects of sexual relationships with a robot, in the context of infidelity and divorce laws. For instance, in this recent article, a scientist argues that legally, sex with a robot is not infidelity, mainly because the robot is not a person (and the robot would just be like any other sex toy).
Now, beyond this legal aspect, from the point of view of the Magisterium (Catholic Church), would sexual activity with a robot count as adultery? To me this is obviously the case, but what's the more technical explanation? Is it because it involves sexual activity outside a marriage relationship and without the purpose of procreation?