What to do..

So me and my bf were eating dinner and I told him that some girl was pregnant that we went to high school with and he started laughing and said “I honestly use to lie to you about talking to her, I tried to get some” saying while we were dating he tried to have sex with her.. then I got mad and she said “sorry forgot I can’t be honest with you.” I I have a right to be mad? I hate that. He wasn’t the best when we dated in high school but we got serious when we turned 18, and changed our entire relationship. Should I be upset? Even tho it happened like 3 years ago? I never even knew...