Best friends?

Kenzie • 21 and happily married! We’ve been trying to have a baby for 2 almost 3 years now with no luck.. I turned here for answers and have gotten a lot of positive help and feedback! 💕
Today I was look through my husbands phone. He's had a girl bestfriend since high school and I was fine with them texting every once in a while and today I saw that they've been texting pretty frequently and kind of flirting. It's made me upset to the point where I want to cry. Idk what to do. I don't want to fight or make him feel like I don't trust him. Suggestions?