Are my feelings valid

Just wondering if how I'm feeling is normal or if I'm over sensitive. Dating a guy for over 4 years, he cheated in the beginning of our relationship, he has a friend he dated in high school and college, she's married two kids, I recently found out they had an affair my guy and her about 3 years before we got together, she's still with her husband whom has no idea, they make plans for the kids playdates, I want him to end the friendship I am not comfortable with it what so ever. Am I wrong?