The counselor encouraged him to open his heart about the traumatic experience he had been carrying for years.

open 的意思是"打开"，这里用作动词，表示"敞开"。 his 是代词 he 的所有格形式，意思是"他的"。 heart 的本义是"心脏"，引申为"内心、情感"。 open his heart 是一个固定短语，意思是"敞开心扉"，指愿意分享内心深处的想法和感受。