Next time you see him and he mentions sex or showers or any of that put this thought in your mind and nothing else..it's just a thought and will help keep you on the task at hand and not in the shower with him..
Imagine yourself standing in front of him, facing him..looking into those big eyes of his, looking at that strapping "stud" of a man...glance over to his right and see OW's face, then look back at him and take one step back then kick him in the nuts...
Now this is just fantasy..it's nothing but thoughts...no actions are required.
he's using you.
What he is doing borders on mental abuse IMO. he's playing you.