It is not a simple matter to judge whether a guy is jealous or not, because everyone's expressions and feelings are different. Here are some signs that may indicate jealousy in a guy, analyzed in multiple dimensions and breadth:
Verbal expression
He may say something sarcastic, cold, or negative. For example, he may taunt you for associating with other boys, or behave coldly when you refer to other boys.
Behavioral changes
If a guy suddenly starts avoiding you or doesn't feel comfortable talking to other guys, then he may be jealous. In addition, he may become more critical of you or find fault with you.
Emotional responses
Jealous boys may show strong emotional reactions, such as anger, frustration, or anxiety. He may be unhappy with your behavior or upset about your emotional state.
Social** activities
If a guy suddenly starts posting some sad or angry states on social **, or frequently likes or comments on you, then he may be trying to get your attention and express his displeasure.
Body language
A jealous guy may express his displeasure through body language. He may avoid eye contact with you or appear nervous when you talk to other guys.
Note that these signs are not 100% sure that a guy is jealous, as everyone expresses it differently. The best way to do this is to communicate with him directly and ask him how he feels.
If you find that he is jealous, then you can try to solve the problem through communication, understanding, and respect.