Trying to read into someone else’s thoughts or feelings about you causes all sorts of problems in relationships, and it’s not good for you. So please don’t do it!
If your guy is a little withdrawn and you choose to believe it’s because he’s losing interest in you and therefore start to pull back from him, you’ll send him a message that you don’t really care about him. Which may, in turn, cause him to break up with you. When the truth was he had a huge problem at work that had been weighing on his mind, and what he really needed was for you to be supportive.
What I’m trying to say is if you decide he’s thinking one thing and you’re wrong, it will cause you to react inappropriately. Which will cause him to respond to you differently. No matter how well you think you know him, you can never know what he is thinking or feeling unless he tells you.
Keep your insecurities out of it and take people at face value. Never assume that you know what anyone is thinking or feeling. Don’t react to anything that you have not confirmed to be a fact. That’s the way to have happier relationships.