Did you ever really get "over it"?

my husband and I have had our fair shares of infidelity. After years and years of fighting over it, I felt I was over the pain I went through when he cheated on me. I got comfortable with joking about them because it has been years and years since they happened, those other women don't matter anymore. I thought I had gained my husband's trust back when we recently met a girl that he is clearly attracted to. I have started feeling completely insecure about our relationship and even suspect him cheating on me. Am I just being crazy and having all these suspicions because it has happened in the past, but it's really not? Or should I go with my gut instict and investigate a little more?