Trouble in paradise

Hey ladies. I need some advice. I had written a long while back about something's going on at home. Back at the end of August early September I caught my husband having an inappropriate string of conversations with his cousins wife. I approached both of them and they both claimed that nothing was going on, my husband apologized and she said it shouldn't have been taken that way and that it was absolutely nothing and apologized. The cousin and my husband are best friends, they're more like brothers. And the wife has been around them both for years and apparently they all have been through so much with each other.

Fast forward to now; I'm currently 13.5 weeks pregnant and we had our gender reveal last weekend. We had a group chat going between us. He was getting texts from her and they were going back and forth while not in the group chat. Come the day of the party there was some major flirting going on. People were drinking and me being the sober one along with one of my friends, noticed it. I didn't say anything at the time because I didn't want to cause a scene. Me being crazy and hormonal went through my cell phone account and looking at his messages and they text back and forth all the time, mostly in the morning early afternoon, but usually first thing in the morning.

I mentioned something again to my husband about it and hes telling me it's nothing, he loves me, wants me, wouldn't be with me if he didn't and that she is his best friend and has saved him so many times and loves her like a family member and all of this other stuff.

Okay great. But I'm you're wife, I'm supposed to be your best friend, I'm supposed to be the person you talk to about everything and first thing in the morning. Please have some respect for me and stop talking to her. Just drop it. Any kind of relationship/friendship I had with really any guys has stopped since we got serious/married ect. Am I overreacting or am I wrong. I need some advice because I'm at a total loss on what to do here.