I think it may be time for a new job OP.

Who knows he still may be whacking by the time his feeding time comes around on your next shift.

My work we were to leave and give them privacy. If they were competent enough (I worked with developmentally disabled clients), we were able to explain to them when that behavior was appropriate and when it wasn't. We also had to explain that sort of stuff if they were dating someone and wanted to have sex... Lol I can't imagine a policy that forces you to sit while they do that. I'd leave and come back.

is there a policy that states he needs to pretend not to notice also?

you should of told him how much of a jerk off he is being Lmfao

I'm fairly sure you're perfectly welcome to leave if a resident is jerking off--and actually, you're supposed to in order to give them privacy? I used to be a resident assistant and there were no rules about staying in the same room as them even if we felt uncomfortable.

They need to change the policy

Sorry, scrolled to the bottom of the comments. At least their policy isn't that you have to help them finish :P

The guy is entitled to do so but you should talk to your boss. You should be allowed to leave him to it and come back later. That situation must make everyone feel really uncomfortable and awkward.

I used to be a caregiver, it's definitely a unique job. OP, just remember that these patients are still people, I know this career path offers some interesting scenarios, so always remember that. It'll get you through the more, erm, delicate moments. And remember to keep everything as professional and as dignified as possible. :)