I'm going to ask my husband to stop talking to my sick ex
Does your husband really talk to your ex?
I think he does because I've seen them together.
You can't really tell your husband what to do. He's allowed to have friends. Maybe you can let him know how it makes you feel if it's hurtful.
I don't want him talking to my ex, but I don't think he cares.
You shouldn't expect that your husband will listen to all the things you say if you're trying to dictate his behavior. You should communicate with him openly about his friendships, but not try to force him to behave in a certain way.