Reading faces is very hard because you can't know if they have a problem with you or just suddenly thought of something that caused them to react that way. The best way is to ask questions after you register a change in both face and tone of voice, other body language, conversation, etc. If it is a big or obvious change, you just smile and say something like, "What was that?"

It is the other person's job to tell you if they have a problem with you or what you are saying, not yours to read their face and "interpret" them. Only they can know for sure what is going on with them. If a change affects you, ask them, "I'm worried that I've said something wrong that has upset you. . ."