Unfortunately some people do pretend in order to avoid conflict or upsetting the other person. If you feel you are being annoying, instead of asking them, just back off from the situation and see if it improves.
I find it's easier to tell when someone's annoyed during conversation simply by the way they are talking. But it's hard when they aren't, actions aren't usually as clear. In my experience people who are annoyed will try to change the conversation, avoid forwarding the conversation, or will simply ignore or pretend not to hear. Some people will also have a tone in their voice indicating that they're not interested.