Husbands best friend is a girl

I need advice before I explode.
My husband has a female best friend. She lives out of state, but when she comes home it is top priority that he sees her. They have been friends for years now, since college days. He is now 30. When we first started dating he introduced me to her and we got along pretty well. As the relationship continued and we got closer their relationship began making me uncomfortable. For example they would create snap chats hugging each other and with kissy faces, and she would post picture on her social media with captions such as “Happy Birthday Booboo”. Alao texting her about her personal life and asking if a dress was cute or appropriate to wear to our engagement and wedding...
Also he fell asleep at her brothers house one day when they all went out, and that pushed me over the edge honestly. That is when I first expressed my discomfort about this relationship. He was upset at the fact that I would even instigate and assume anything and it was dropped. Months later (we were engaged at this point) we all went out together. There was a moment where we were all in the elevator together and when we got out I looked back and my fiancé and her were not behind me. Rather they were by the elevator as she was whispering in his ear about how I said something to her that made her uncomfortable. At this moment I screamed out as I walked away, “ one second guys the best friends are sharing secrets by the elevator” (immature I know, but I was deeply hurt). She then came up to me and said “******* stop this **** right now, you’re ruining our friendship”. The next day she continued on by texting my fiancé while I was with him explaining her hate for me and calling me things like crazy. My husband simply ignored it. Her and I have had many conversations on the phone and tried to squash it but now it’s just always awkward when we see each other. My husband ignores her calls as a way to make me feel better and calls her later but this honestly makes me feel even worse. I have recently began feeling better about it but she came home for the holidays recently and I lost it again.

My husband one day took really long to get home. He simply explained he got caught by a train, traffic, etc..... the night went on and everything was fine.

As we were sitting on the couch he received a message on his laptop and I noticed a text from her saying did I forget my bag? I asked what she meant and he explained that he had given her a ride from the suburbs to the city. I was extremely angry that he didn’t tell me? He purposely left that part of the story out about why he was late because he “assumed” I would be upset but failed to realize the shadiness is what hurt me. He justified but explaining “I don’t need to know every detail of his life”. I got in my car the next day and she wrote on steamed windows her name. It’s almost as if she WANTED TO GUARANTEE I knew she got a ride. Am I crazy for thinking this way?

We hung out with them some more and there was an instance where he had her phone and she allowed him to go through it. He was searching his name in her messages and it was making me extremely uncomfortable. There was even a message in there that said “remember when you got anon to share Steve’s (my husband) secrets”

This relationship is Allllll I think about. I feel so confused and hurt and I don’t even know if I have a reason too. I’m so convinced in my mind they want each other and I can’t stop. Whenever they disappear I am so afraid they are cheating and it makes me want to crawl out of my skin and just cry. I don’t know what to do anymore. I am starting therapy because of this because I’m at the point where I am convinced I am crazy. Every time I bring it up to him he gets defensive and doesn’t want to listen. What should I do? Am I feeling all the wrong things or are the things I listed reasonable enough to make me not happy about their friendship. Please help me.