Romantic Relationship Insecurity

I find myself to be a confident and secure woman in many ways. I’m successful professionally, have many wonderful friends, have accomplished a lot I’m proud of, and have many interests. That being said, every time I am dating a man, I become insecure. I can’t handle my significant other having female friends, looking at other women, and especially not flirting with other women. I am divorced and have been dating someone for about a year. He is great, but I don’t want my insecurity to harm our relationship. Do you have any strategies you may suggest on how I may overcome this? Thank you for your insights.