Husband told me he cheated on me in high school

My husband and I dated in high school, got married right after we graduated. It’s been 5 years since then. He came to me crying the other night and said he wanted to tell me something. He said he cheated on my a couple times in high school. I asked why he did, he said he was immature and stupid but didn’t really have a reason. I asked why he told me and he said he always felt guilty about it and said I deserved to know even if it was years ago. I don’t even know how to feel to be honest. I’m glad he told me, sure. And it was years ago in high school. But it’s definitely upsetting still. Would you be mad? Should this be a deal breaker? Ugh